Reducing Risk Where Tectonic Plates Collide—

A Plan to Advance Subduction Zone Science

Circular 1428

U.S. Department of the Interior

U.S. Geological Survey
Front cover. A U.S. Geological Survey scientist surveys Loowit Creek drainage on Mount 

St. Helens, part of a long-term project to track sediment erosion and deposition in the channel. 

View to the north, with Spirit Lake and Mount Rainier in the background. U.S. Geological Survey 

photograph by Kurt Spicer.
Reducing Risk Where Tectonic Plates 

Collide—A Plan to Advance Subduction 

Zone Science

By Joan S. Gomberg, Kristin A. Ludwig, Barbara A. Bekins, Thomas M. Brocher, 

John C. Brock, Daniel Brothers, Jason D. Chaytor, Arthur D. Frankel, 

Eric L. Geist, Matthew Haney, Stephen H. Hickman, William S. Leith, 

Evelyn A. Roeloffs, William H. Schulz, Thomas W. Sisson, Kristi Wallace, 

Janet T. Watt, and Anne Wein

Circular 1428

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

RYAN K. ZINKE, Secretary

U.S. Geological Survey

William H. Werkheiser, Acting Director

U.S. Geological Survey, Reston, Virginia: 2017

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

resources, natural hazards, and the environment—visit https://www.usgs.gov/ or call 1–888–ASK–USGS.

For an overview of USGS information products, including maps, imagery, and publications, 

visit https://store.usgs.gov.

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Gomberg, J.S., Ludwig, K.A., Bekins, B.A., Brocher, T.M., Brock, J.C., Brothers, Daniel, Chaytor, J.D., Frankel, A.D., 

Geist, E.L., Haney, Matthew, Hickman, S.H., Leith, W.S., Roeloffs, E.A., Schulz, W.H., Sisson, T.W., Wallace, Kristi, 

Watt, J.T., Wein, Anne, 2017, Reducing risk where tectonic plates collide—U.S. Geological Survey subduction zone 

science plan: U.S. Geological Survey Circular 1428, 45 p., https://doi.org/10.3133/cir1428.

ISSN 1067-084X (print) 

ISSN 2330-5703 (online) 

ISBN 978-1-4113-4150-0
iii

Contents

Executive Summary.......................................................................................................................................1

Introduction.....................................................................................................................................................3

A Growing Sense of Urgency .............................................................................................................8

Role of the USGS and Its Partners.....................................................................................................8

A Plan to Advance Subduction Zone Science for Society ............................................................9

Stakeholder Needs........................................................................................................................................9

Science Themes of the Subduction Zone Science Plan.......................................................................12

Theme 1: Advancing Observations and Models of Subduction Zone Processes....................12

A Foundation of Accomplishments and Capabilities ...........................................................12

Gaps in Knowledge and Capabilities, and Scientific Research Frontiers........................13

Characterizing Past Hazardous Events to Forecast the Future Using 

Onshore Clues......................................................................................................13

Refining Subduction Zone Earthquake Chronologies Using Offshore Clues ..........13

Understanding Cycles of Volcanic Eruptions...............................................................14

Forecasting Destructive Earthquake-Triggered Landslides .....................................14

Anticipating Great Subduction Zone Earthquakes and Tsunamis Using 

Seafloor Observations........................................................................................14

Determining the Role of Water in Subduction Zone Processes ...............................14

Addressing Multidisciplinary Questions About Sediment Transport.......................17

Mapping Bathymetry and Topography from the Deepest Seafloor to 

Continental Interiors ...........................................................................................17

Key Questions, Investments, and Products...........................................................................17

Theme 2: Quantifying Natural Hazards and Risk ...........................................................................18

A Foundation of Accomplishments and Capabilities ...........................................................18

Gaps in Knowledge and Capabilities and Frontiers of Scientific Research ....................21

Communicating Hazard and Risk to Communities.......................................................21

Discriminating Between Causes and Effects of Subduction Zone 

Processes and Climate Change........................................................................21

Assessing the Nation’s Energy and Mineral Resources............................................21

Assessing the Potential for Submarine Landslides ....................................................22

Accounting for Locally Hazardous Tsunamis...............................................................22

Predicting How the Built Environment Will Respond to Strong 

Earthquake Shaking............................................................................................22

Key Questions, Investments, and Products...........................................................................23

Theme 3: Forecasting and Situational Awareness........................................................................24

A Foundation of Accomplishments and Capabilities ...........................................................24

Gaps in Knowledge and Capabilities and Frontiers of Scientific Research ....................25

Developing Tools for Cascading Hazards .....................................................................25

Forecasting Coastal Land-Level Changes ....................................................................26

Assessing the Effects of Subduction Zone Events on Ecosystems..........................27

Increasing the Reliability of Earthquake and Tsunami Warnings.............................28

Providing Reliable, High-Fidelity Volcano Warnings ..................................................28

Projecting Ash Cloud Trajectories More Accurately..................................................29
Providing Spatially Varying, Regionally Specific Aftershock Forecasts .................29

Key Investments and Products................................................................................................31

National and Global Partnerships.............................................................................................................31

Current and Future Domestic Institutional Partners.....................................................................31

Shared Scientific Infrastructure ......................................................................................................32

Onshore Monitoring and Laboratories..........................................................................32

The Offshore Frontier.......................................................................................................32

Information Technology and Management ..................................................................32

International Activities.......................................................................................................................35

New Community Resources and Engagement .......................................................................................35

Products ...............................................................................................................................................35

Outreach and Education....................................................................................................................37

Data Management Plan.....................................................................................................................38

Acknowledgments.......................................................................................................................................38

References Cited..........................................................................................................................................38

Appendix 1. Selected Current and Potential Partnerships................................................................42

U.S. Governmental, Professional, and Private Entities.................................................................42

Federal Agencies.......................................................................................................................42

State, Commonwealth, Territorial............................................................................................43

Professional and Academic Organizations and Private Companies.................................43

Monitoring Networks .........................................................................................................................44

Offshore Facilities...............................................................................................................................44

Appendix 2. International Monitoring, Disaster Mitigation and Response, and 

Capacity Building............................................................................................................................45

Figures

1. Map showing the Pacific Ocean basin and surrounding “Ring of Fire” 

subduction zones, where the tectonic plates collide, creating volcanoes, 

earthquakes, tsunamis, and mountainous landslide-prone terrain .....................................4

2. Example of a landslide susceptibility map after a period of heavy rainfall ......................19

3. Map showing tsunami wave height estimates for Seaside, Oregon, calculated 

for a range of likely earthquake sources of magnitude 8–9 ................................................20

4. Simplified map of ground-based volcanic hazards from an eruption of the most 

threatening volcano in Cascadia: Mount Rainier, Washington...........................................26

5. Photos showing landslides in Seattle, Washington..............................................................27

Table

1. Potential products and key investments for building resilience ..........................................2

iv
v

Sidebar Stories

Schematic Cross Section of a Typical Subduction Zone ............................................... 6

Historic Subduction Zone Earthquakes, Eruptions, Landslides, and 

Tsunamis in the United States............................................................................... 7

Neighborhood-Scale Earthquake Ground Motion Maps ............................................. 11

Tremor and Slow Slip Illuminate Potential Earthquake Faults .................................... 13

The Onshore and Offshore Records of Great Earthquakes ......................................... 15

Seafloor Instrumentation and the 2011 Magnitude 9.0 Tōhoku, Japan, 

Earthquake.............................................................................................................. 16

Using Bathymetric and Topographic Data to Identify Local Tsunami Hazards ........ 23

Regional Workshop to Develop the SAFRR Tsunami Scenario................................... 28

Satellites Identify Areas of Tsunami Inundation............................................................ 29

Volcanic Ash Forecasting.................................................................................................. 30

Offshore/Onshore Earthquake Hazard Experiment in the Caribbean ........................ 33

Seafloor Real-Time Monitoring......................................................................................... 34

Partnering with USAID for Science and Humanity ....................................................... 36

U.S. Geological Survey research geophysicist Kate Allstadt assists students in the GeoGirls program 

to deploy a seismometer at Mount St. Helens, Washington. The girls collected the seismometers two 

days later and analyzed the earthquake information recorded by the instruments. USGS photograph 

by Carolyn Driedger.
U.S. Geological Survey scientists Randy Jibson and Jonathan Godt 

investigate the Seaside landslide that was triggered by the 2016 

magnitude 7.8 Kaikoura, New Zealand, earthquake, along a fault 

that experienced significant surface offsets. USGS 

photograph by Kate Allstadt.
Reducing Risk Where Tectonic Plates Collide—A Plan to 

Advance Subduction Zone Science

By Joan S. Gomberg, Kristin A. Ludwig, Barbara A. Bekins, Thomas M. Brocher, John C. Brock, 

Daniel Brothers, Jason D. Chaytor, Arthur D. Frankel, Eric L. Geist, Matthew Haney, Stephen H. Hickman, 

William S. Leith, Evelyn A. Roeloffs, William H. Schulz, Thomas W. Sisson, Kristi Wallace, Janet T. Watt, 

and Anne Wein

Executive Summary

When tectonic plates collide, the thrusting of one plate 

over the other (a process called subduction) leads inevitably to 

the world’s largest earthquakes, powerful tsunamis, explosive 

volcanic eruptions, and massive landslides, both on land and 

offshore. As recent subduction zone earthquakes and tsunamis 

in Sumatra (magnitude [M] 9.1, 2004), Chile (M8.8, 2010), 

and Japan (M9.0, 2011); volcanic eruptions in the United 

States (Mounts St. Helens, Washington, 1980; Redoubt, 

Alaska, 1989, 2009) and Pinatubo in the Republic of the Philippines (1991); and major landslides (Oso, Washington, 2014) 

have demonstrated, these events have cascading consequences 

that reverberate around the globe.

Future such events are inevitable in our Nation’s subduction zones, which encompass the States of Alaska, Washington, Oregon, northern California, commonwealths of Puerto 

Rico and the Northern Mariana Islands, and territories of 

American Samoa and Guam. Subduction zone events pose significant threats to lives, economic vitality, cultural and natural 

resources, and quality of life of the Nation’s communities.

The U.S. Geological Survey (USGS) serves the Nation 

by providing reliable scientific information and tools to build 

resilience in communities exposed to subduction zone earthquakes, tsunamis, landslides, and volcanic eruptions. Improving the application of USGS science to successfully reduce 

risk from these events relies on whole community efforts, with 

continuing partnerships among scientists and stakeholders, 

including researchers from universities, other government labs 

and private industry, land-use planners, engineers, policymakers, emergency managers and responders, business owners, insurance providers, the media, and the general public.

Motivated by recent technological advances and 

increased awareness of our growing vulnerability to subduction-zone hazards, the USGS is uniquely positioned to take a 

major step forward in the science it conducts and products it 

provides, building on its tradition of using long-term monitoring and research to develop effective products for hazard 

mitigation. This science plan provides a blueprint both for 

prioritizing USGS science activities and for delineating USGS 

interests and potential participation in subduction zone science 

supported by its partners.

The activities in this plan address many USGS stakeholder needs:

• High-fidelity tools and user-tailored information that 

facilitate increasingly more targeted, neighborhoodscale decisions to mitigate risks more cost-effectively 

and ensure post-event operability. Such tools may 

include maps, tables, and simulated earthquake 

ground-motion records conveying shaking intensity 

and frequency. These facilitate the prioritization of 

retrofitting of vulnerable infrastructure;

• Information to guide local land-use and response 

planning to minimize development in likely hazardous zones (for example, databases, maps, and scenario 

documents to guide evacuation route planning in communities near volcanoes, along coastlines vulnerable to 

tsunamis, and built on landslide-prone terrain);

• New tools to assess the potential for cascading hazards, 

such as landslides, tsunamis, coastal changes, and 

flooding caused by earthquakes or volcanic eruptions;

• Geospatial models of permanent, widespread land- and 

sea-level changes that may occur in the immediate 

aftermath of great (M≥8.0) subduction zone earthquakes;

• Strong partnerships between scientists and public 

safety providers for effective decision making during 

periods of elevated hazard and risk;

• Accurate forecasts of far-reaching hazards (for example, ash clouds, tsunamis) to avert catastrophes and 

unnecessary disruptions in air and sea transportation;

• Aftershock forecasts to guide decisions about when and 

where to re-enter, repair, or rebuild buildings and infrastructure, for all types of subduction zone earthquakes.
2 Reducing Risk Where Tectonic Plates Collide—A Plan to Advance Subduction Zone Science

Meeting the above needs of stakeholders aligns with the 

three themes of the plan: (1) improving our observations and 

models of subduction zone processes; (2) analyzing natural 

hazards and risk; and (3) providing forecasts and situational 

awareness. Realization of these scientific and technological 

goals will lead to innovative, resilience-building products, 

broadly summarized in table 1. All the scientific inputs noted 

have some relevance to all the products in the table.

Table 1. Potential products and key investments for building resilience.

Products Description Primary scientific inputs Key 

investments* Application

High-resolution hazard 

and risk assessments 

Neighborhood-scale estimates of 

earthquake shaking, tsunami 

inundation, landslides, potential 

volcanic eruptions and lahars, and 

their consequences.

High-resolution topography, 

onshore and offshore; 3-D 

models of Earth structure; 

well-characterized faults, 

unstable slopes, and active 

volcanoes.

A–I Building design codes, 

prioritized retrofitting, urban planning, and evacuation 

routing.

Scenarios Science-based simulations of 

hypothetical subduction zone 

events and their impacts.

Chronologies of past subduction 

zone events from geologic 

field and laboratory studies. 

G, H Improved mitigation 

strategies.

Warning systems Notice of strong earthquake 

shaking, volcanic eruptions and 

ground-failures, tsunamis, and 

landslides.

Multidisciplinary monitoring systems, onshore and offshore. A, B, C Rapidly implemented 

life- and propertysaving measures.

New types of forecasts Updated projections of aftershocks, 

landslides, volcanic debris flows, 

and ash clouds.

Rapidly acquired satellite and 

surface measurements.

A, B, C, I Safer, faster, and more 

cost-effective response and recovery.

Novel assessments of 

cascading subduction 

zone events

Likelihoods of landslide-triggered 

tsunamis; earthquake-induced 

coastal land-level changes, 

flooding, and erosion. 

Computer models simulating 

linked processes.

F, I Rapid and effective 

mitigation, response, 

and recovery.

*Key investments for forefront science and products:

A. Targeted, dense, land-based networks for monitoring 

earthquake, volcanic, and ground-failure processes.

B. Routine operation of multidisciplinary monitoring.

C. Partnerships to develop and operate permanent 

seafloor seismic and geodetic monitoring 

instrumentation.

D. Offshore sediment-core samples, images of 

subsurface geologic structures, temporary 

geophysical deployments.

E. High-resolution, multibeam bathymetry offshore, 

adjacent to airborne and space-based topographic 

imagery onshore.

F. Observationally constrained, three-dimensional 

models of the Earth’s interior.

G. Expanded geologic field programs.

H. Laboratory capabilities for dating and analyzing the 

physical properties of rock samples.

I. Synoptic, integrative multidisciplinary 

computer models.

U.S. Geological Survey scientists tour the construction site of 

the new Amazon.com campus in downtown Seattle, Washington, and learn about how USGS information has been used to 

make the facilities more resilient when shaken by earthquake 

waves. USGS photograph by Joan Gomberg.
Introduction 3

Introduction

We live on a dynamic planet, which is constantly in motion at multiple scales, from 

changing daily weather patterns to the shifting of massive tectonic plates. And, yet, nowhere is 

the Earth more geologically active than in regions where these tectonic plates collide, which are 

known as subduction zones (see sidebar about subduction zones on p. 6). Much of the United 

States lies within subduction zones: Alaska, Washington, Oregon, and northern California, the 

commonwealths of Puerto Rico and the Northern Mariana Islands, and the territories of American Samoa and Guam are all situated within subduction zones (fig. 1). Regions surrounding 

the Pacific Ocean where plates collide comprise the “Ring of Fire” because of the prevalence 

of volcanoes and earthquakes; outside the United States, Ring of Fire countries include Japan, 

the Republic of the Philippines, and the Republic of Indonesia. All these countries face subduction zone hazards, along with many nations in the Caribbean, eastern Indian Ocean, and around 

the Mediterranean Sea. In these areas, the constant motion of the Earth, usually 

slow and inexorable, can create catastrophes in an instant: the world’s 

largest earthquakes can rupture the seafloor, generating powerful tsunamis; explosive volcanoes can thrust ash into the 

sky; landslides can reshape entire landscapes both on 

land and offshore. The tremendous magnitudes and 

frequencies of these hazardous events are unique 

to subduction zones, and they can have cascading consequences that reverberate around the 

globe. Subduction zone events pose significant threats to lives, property, economic 

vitality, cultural and natural resources, and 

quality of life.

Over the past 55 years, the Nation 

has experienced the 1964 magnitude (M) 

9.2 Alaska earthquake, the 1980 eruption of Mount St. Helens, the 2014 Oso 

landslide, and numerous other smaller, 

but locally significant, subduction zone 

events (see sidebar about historic events 

on p. 7 ). Worldwide, in less than the span 

of a generation, we have witnessed firsthand 

the devastating power and global impact of 

subduction zone events: in 1991, the cataclysmic 

eruption of Mount Pinatubo in the Republic of the 

Philippines led to evacuation of 20,000 people and 

a sulfuric haze caused global temperatures to drop by 

0.5 °C (0.9 °F) for the following two years. In 2004, the 

M9.1 Sumatra–Andaman earthquake and ensuing Indian Ocean 

tsunami resulted in more than 200,000 deaths in 14 countries, damaged 

fisheries in Japan, and triggered earthquakes as far away as Alaska. In 2010, offshore Chile—where building standards and preparedness levels are comparable to those in the 

U.S.—a M8.8 earthquake ruptured the seafloor. The quake triggered a tsunami, which damaged 

coastal towns and affected ports as far away as San Diego, California. The initial earthquake 

was followed by several M~7 aftershocks in the subsequent months, which struck immediately beneath population centers and caused more damage locally than the mainshock. Nearly 

525 people died, and estimated economic losses range from $15–30 billion (U.S. dollars). In 

2011, the M9.0 Tōhoku earthquake jolted Japan: skyscrapers swayed and pedestrians ran from 

falling debris during five minutes of sustained shaking, and the tsunami, with wave heights 

taller than 30 meters (100 feet), flung boats atop houses, flooded rural farms with seawater, and 

caused a meltdown at the Fukushima Daiichi Nuclear Power Plant. Nearly 16,000 people died, 

and the damages totaled more than $220 billion.

The Blue Marble. 

Image by NASA/Goddard 

Space Flight Center
4 Reducing Risk Where Tectonic Plates Collide—A Plan to Advance Subduction Zone Science

140°W 160°W 180°W 160°W 

60°N

40°N

20°N

0°

20°S

EURASIAN PLATE

AUSTRALIA

PLATE

PHILIPPINE 

PLATE

8,000 6,000 5,000 4,000 3,000 2,000 1,000 500 1,000 2,000 3,000 4,000

Topography: depth and elevation in meters

0

Volcano

Subduction zones that are part of the 

United States and its territories

Earthquake, magnitude 5 or greater

Plate tectonics

Divergent (sea-floor spreading) and 

transform fault boundaries—Red 

lines mark spreading centers. Thin 

black line marks the plate boundary, 

whether sea-floor spreading center 

or transform fault

EXPLANATION

ALAS

MARIANAS

(Northern Marianas,

Guam)

Tonga

(American

Samoa)

Figure 1. The Pacific Ocean 

basin and surrounding “Ring of 

Fire” subduction zones, where the 

tectonic plates collide, creating 

volcanoes, earthquakes, tsunamis, 

and mountainous landslide-prone 

terrain. Subduction zones are shown 

by high densities of earthquakes and 

volcanoes. Subduction zones within 

the United States and its territories 

are shaded pink. Other types of plate 

boundaries are shown with thin red 

lines. Colors reflect topography and 

bathymetry; darker blues and purple 

offshore are deeper water, while 

brown and orange are mountain 

ranges. Map simplified from Simkin 

and others (2006).
Introduction 5

140°W 120°W 100°W 80°W 60°W

0

0

200

200

400

400

600

600

800

800 1,000

1,000 1,200 KILOMETERS

1,200 KILOMETERS EQUATOR

70

60

50 403020 10

SOUTH

AMERICA

PLATE

NORTH AMERICAN PLATE

NAZCA PLATE

PACIFIC PLATE

COCOS PLATE

CARIBBEAN PLATE

JUAN DE FUCA PLATE

SKA CASCADIA

CARIBBEAN

(Puerto Rico,

U.S. Virgin Islands)
6 Reducing Risk Where Tectonic Plates Collide—A Plan to Advance Subduction Zone Science

Schematic Cross Section of a Typical Subduction Zone

Melting

Volcano

Ash cloud

Upper plate

Motion Plate

Landslides Tsunami

Subducting plate

Locked interface

Great earthquakes

Outer-rise

Intra-plate

Fluids

When tectonic plates converge (illustrated by the thick black arrows on either side of the image), one plate slides 

beneath the upper plate, or subducts, descending into the Earth’s mantle at rates of 2 to 8 centimeters (1–3 inches) per 

year (red-brown slab with skinny arrow shows direction of motion). At shallow depths, less than about 25 kilometers 

(16 miles), the interface between the plates may become stuck, or “locked,” and stresses build along these giant faults 

until they exceed the fault’s strength and break free, causing an earthquake. These subduction zone earthquakes are 

the largest on Earth because of the massive size of the faults they may break. Other types of hazardous subduction zone 

earthquakes include deep, “intra-plate” earthquakes that occur within the subducting plate below about 30 kilometers 

(19 miles) below the surface or shallow, “outer-rise” earthquakes that occur just a few kilometers below the surface, 

where the plate begins its descent. Each of these types of subduction-zone earthquakes, along with more ubiquitous 

shallow earthquakes within the continental crust of the upper plate, has different characteristics. Large subduction 

zone earthquakes can suddenly elevate or depress the seafloor, creating a tsunami. Trenches form where the subducting plate begins its descent and can be as much as 11 kilometers (7 miles) deep. Thick layers of sediment may accumulate from the continental shelf to the trench, and may contain secondary faults that splay off the main interface fault 

(represented by the lines in the yellow-orange sediments in the figure). Trench sediments and the rocks of the subducting plate contain water that subduction transports to depths (labeled “fluids” on the diagram), where higher temperatures and pressures lead to melting of the subducting plate and mantle rocks, generating magma. The buoyant magma 

rises up to the surface, forming chains of volcanoes.

Scientists from the 

U.S. Geological Survey and 

the University of Washington deploy instruments 

in Lake Washington and 

Puget Sound, near Seattle, 

Washington, as part of an 

experiment to characterize the Seattle Fault and 

the potential for submarine 

landslides. U.S. Geological Survey photographs by 

Scott Bennett.
Executive Summary 7

Historic Subduction Zone Earthquakes, Eruptions, Landslides, and Tsunamis in the 

United States

The most recent magnitude 9 or larger (M>9) subduction 

zone earthquakes and tsunamis in the United States were 

the M9.0 earthquake on January 26, 1700, in the Pacific 

Northwest (Cascadia) and the M9.2 earthquake in Alaska 

on March 27, 1964. Both of these events left deposits in 

coastal sediment layers, indicating widespread submergence of the coast.

Tokyo (EDO)

Tokyo

N

0 500 MILES

0 500 KILOMETERS

Japanese historical accounts from 1700 document flooding 

along nearly 1,000 kilometers (about 620 miles) of Japan’s 

coast (locations circled above on the historical and inset 

maps above) caused by the tsunami following the M9.0 

Cascadia earthquake. From Atwater and others (2015).

On March 22, 2014, the Oso landslide in Washington State, seen in the aerial photograph above left, sent 18 million tons of 

sediment racing downhill at speeds averaging 64 kilometers (40 miles) per hour before stopping 1.5 kilometers (0.9 miles) 

away. It claimed 43 lives and 35 homes, covered a highway, and dammed a river. Economic losses exceeded $150 million. 

Photograph by M. Reid, USGS.

Shaking during the 1964 Alaska earthquake was felt as 

far away as Seattle, Washington, and its tsunamis caused 

129 fatalities and about $2.3 billion in property losses (2013 

dollars). This massive shift of the Pacific Plate also caused 

widespread, permanent land-level changes, which are still 

visible at Girdwood, Alaska, where the land dropped almost 

2 meters (6.6 feet); the sudden incursion of seawater killed 

the trees but left them standing, resulting in a “drowned” 

forest (above). Photograph from P. Haeussler, USGS.

On May 18, 1980, Mount St. Helens (above) erupted in 

Washington State, setting a U.S. historic record for the largest volcano-related number of fatalities (57) and property 

loss ($1.1 billion in 1980 dollars). Following one of the largest 

landslides in recorded history, it erupted with a blast that 

cleared 596 square kilometers (230 square miles) of forest, 

sent mud flows tens of miles down multiple drainages, and 

blanketed areas hundreds of miles downwind with ash. 

Photograph is figure 11 from Lipman and Mullineaux, 1981; 

copyright Keith Ronholm, 1980, published with permission. 
8 Reducing Risk Where Tectonic Plates Collide—A Plan to Advance Subduction Zone Science

A Growing Sense of Urgency

Mega-disasters like the events in Sumatra, Chile, and 

Japan remind us of nature’s power and have called into question our resilience to future events. In the Nation’s subduction 

zones, the probability is high that at least one major earthquake, tsunami, volcanic eruption, or landslide will occur in 

the coming decades. Experience also has shown that smaller 

but more frequent events may be more hazardous locally than 

the larger, rarer ones. Localized volcanic hazards include 

lahars, landslides, lava and pyroclastic (avalanches of hot ash 

and gas) flows, toxic gas emissions, air blasts, and eruptive 

projectiles that may destroy structures and wildlife in their 

paths. Major eruptive events may be preceded by unrest lasting hours to months, presenting communications challenges 

to local populations. Locally destructive tsunami waves may 

be generated by rapid slip on nearshore faults or by submarine 

landslides. Landslides are particularly acute near subduction 

zones where geologic processes create steep, rapidly evolving topography. Moderate earthquakes in the M5–6 range 

that strike just beneath urban centers may disrupt all activity 

within them, sometimes causing major human and economic 

losses. The past five years have seen a confluence of activities 

contributing to a growing sense of urgency to prepare for these 

events. Recent media coverage, regional preparedness exercises, and technical advances all point to a unique opportunity 

to leverage interest and concern for subduction zone hazard 

mitigation.

The threat of geologic hazards lurking in the Nation’s 

subduction zones was dramatically highlighted by the Pulitzer 

Prize-winning article, “The Really Big One” (Schulz, 2015), 

about the potential effects of a M9 earthquake in the Pacific 

Northwest’s Cascadia Subduction Zone. The article spurred 

conversation across the country, drew attention to the lack 

of seismic readiness, and magnified concern for the region’s 

capacity to respond to a major event. While the probability of 

a M9 earthquake occurring in the Nation’s subduction zones 

has not changed over the past few decades, the rapid growth of 

populations in these zones and intertwined global economies 

means that increasingly more people and economic assets are 

at risk.

Similarly, the need to prepare for subduction zone 

hazards was underscored by both the 2014 Alaska Shield 

and 2016 Cascadia Rising exercises,1 led by the Federal 

Emergency Management Agency (FEMA), which revealed 

weaknesses in response coordination and public readiness 

messaging. Those exercises focused on the immediate effects 

of great earthquakes on the Nation’s built environment, public 

services, health, and economy, and they highlighted the need 

for effective coordination and integration among authorities 

at all levels—cities, counties, State and Federal agencies, 

the military, and tribal nations, as well as non-governmental 

organizations and the private sector—to conduct successful 

response operations.

1

https://www.fema.gov/cascadia-rising-2016

Technological and scientific advances continue to create 

opportunities to observe and analyze the processes that cause 

natural hazards. These advances also enable the newfound 

knowledge to be translated into quantitative assessments and 

rapidly delivered information about likely effects of unfolding events (that is, situational awareness). These feed into 

decision-support products and effective risk-reduction policies 

and codes that are based on accurate knowledge of the severity 

and possible effects of hazardous events both before and after 

they occur. For example, the U.S. Geological Survey (USGS) 

issues an alert within 30 minutes of an earthquake worldwide, called a Prompt Assessment of Global Earthquakes for 

Response (PAGER) alert, that estimates economic losses and 

fatalities and thereby helps to direct response decisions and 

humanitarian aid. The National Science Foundation (NSF)-

supported Ocean Observatories Initiative operates a cabled 

seafloor observatory that enables scientists to remotely observe 

and monitor, in real time, changes in undersea earthquake, 

volcanic, and other geologic activity in a few areas beneath the 

northeast Pacific Ocean. On the U.S. West Coast, the USGS 

and its partners are prototyping the ShakeAlert earthquake 

early warning (EEW) system, which will deliver warnings 

of impending ground shaking to people and infrastructure in 

harm’s way seconds after an earthquake occurs.

Role of the USGS and Its Partners

The USGS serves the Nation by providing reliable scientific information to describe and understand the Earth in order 

to enhance and protect our quality of life. The USGS Natural 

Hazards Mission Area strives to minimize loss of life and 

property from natural disasters. Addressing this mission leverages the capabilities and expertise of other USGS programs 

that manage water, biological, energy, and mineral resources. 

Activities of the Natural Hazards Mission Area include realtime monitoring of subduction zone processes, which serves 

the goals of increasing scientific understanding, providing 

timely warnings, and delivery of rapid post-event information to decision makers and the public. Other key activities 

that address the USGS’s mission include ongoing geologic 

and geophysical field studies, high-resolution topographic 

mapping, and operation of state-of-the-art laboratories; these 

provide data that underpin the USGS products delivered to 

its stakeholders. USGS scientists from many programs across 

the United States routinely partner with experts at the Federal, 

State, and local levels, and teams from diverse disciplines 

design and implement innovative approaches to help understand hazardous processes. 

Improving the application of USGS science to successfully reduce risk from subduction zone events also relies on 

community efforts, including collaborations among scientists, 

emergency managers, resource managers, and businesses, as 

well as between international, Federal, State, and local authorities. The USGS is uniquely positioned to tackle complex 

scientific questions and work with stakeholders to translate 
Stakeholder Needs 9

improved understanding of hazards in ways that are useful for 

decision-making (Holmes and others, 2013). The USGS, along 

with its partners, brings to bear multiple disciplines, a wide 

array of monitoring capabilities, and unique responsibilities 

to contribute to the safety and resilience of communities and 

resources at risk.

A Plan to Advance Subduction Zone Science 

for Society

The growing recognition of the scale of the threat posed 

by mega-disasters like great subduction zone earthquakes and 

tsunamis, combined with the confluence of activities focused 

on subduction zone hazards, creates a unique opportunity 

to leverage mounting momentum in this field. Recognizing 

this opportunity, USGS has developed this Subduction Zone 

Science Plan as a blueprint both for prioritizing USGS science activities, for delineating USGS resources, and potential 

participation in subduction zone activities supported by other 

agencies. To be most effective, this blueprint must be executed 

in collaboration with researchers from universities, other government labs, and private industry. This plan was undertaken 

by the USGS Natural Hazards Mission Area, and a writing 

team was drawn from multiple disciplines across regionally 

managed science centers. It is intended for current and future 

USGS scientists, USGS leadership, policy makers, colleagues 

in academic institutions, and partner agencies committed to 

advancing subduction zone science and risk reduction.

The Subduction Zone Science Plan addresses the needs 

of stakeholders and collaborators by focusing on three science 

themes: (1) advancing observations and models of subduction zone processes, (2) quantifying natural hazards and risk, 

and (3) forecasting and situational awareness. These three 

themes reflect the priorities outlined in the Natural Hazards 

Science Strategy Plan (Holmes and others, 2013). Each theme 

describes USGS accomplishments and current capabilities, 

discusses specific knowledge and capability gaps and scientific 

frontiers, and concludes with a summary of key questions (in 

the themes 1 and 2 subsections), needed research and facilities 

(investments), and products. Table 1 (on p. 2) broadly summarizes the information products that could be delivered by 

following the Subduction Zone Science Plan, which would lay 

the foundation for resilience-building actions. Key investments suggested for forefront science are listed following 

the table. Specific examples of these products are also found 

throughout the “Science Themes” section, and in the section 

titled “New Community Resources and Engagement.”

The section “National and Global Partnerships” describes 

opportunities to leverage investments in subduction zone scientific research and facilities made by other organizations and 

to build new partnerships and capabilities.

The opportunities described herein build on a strong 

foundation of existing USGS and partner expertise and upon 

current understanding of the geologic hazards associated with 

subduction zones. Significant uncertainty remains, however, 

requiring new research and innovative applications to improve 

accuracy and meet new challenges. Addressing many of the 

gaps in knowledge and capabilities and the scientific frontiers 

identified in this plan will take a concerted effort across the 

USGS and its many partners, yet the Subduction Zone Science 

Plan holds promise to make the Nation more resilient when the 

next subduction zone event strikes, wherever it may occur.

Stakeholder Needs

Earthquakes, tsunamis, volcanic eruptions, and landslides 

are common to subduction zones and can affect extensive 

areas and have far-reaching consequences. Stakeholders that 

benefit from the science detailed in this plan include landuse planners; civil, structural, and environmental engineers; 

policy makers; insurance providers; emergency managers and 

responders; infrastructure operators; business owners; the 

media; and the general public living near subduction zones. 

In addition, to most effectively communicate information, 

advances in the physical sciences must be coupled with socialscience research and scientist-user collaborations. For nearly 

all potentially hazardous subduction-zone events, stakeholders 

need the following products, ordered from long-term planning 

to post-event response and recovery.

Vasily Titov (left, a scientist at the National Oceanic and 

Atmospheric Administration) and Bruce Jaffe (a U.S. Geological Survey scientist) by a tsunami warning sign in Pago Pago, 

American Samoa. The death toll from the 2009 magnitude 8 

Samoa earthquake and tsunami on American Samoa would 

have been in the thousands if people hadn’t known to go to 

higher ground after the earthquake. Photograph by Marie Chan 

Kau, Community and Natural Resources, American Samoa 

Community College.
10 Reducing Risk Where Tectonic Plates Collide—A Plan to Advance Subduction Zone Science

• Tools that provide high-fidelity, user-tailored 

information that facilitate targeted, neighborhoodscale decisions to mitigate risks cost-effectively and 

ensure post-event operability.

• Example need: city officials and engineers prioritize 

spending of a limited budget to retrofit buildings 

and infrastructure to be more resilient to earthquake 

shaking. 

• Requirements to address the need: estimates of 

likely event characteristics (for example, shaking 

intensity and frequency) at the neighborhood scale 

for the wide range of event types, sizes and frequencies. Information may be conveyed in maps, tables, 

or simulated shaking records (see sidebar about 

neighborhood-scale maps on next page). 

• Information to guide local land-use and emergency 

response planning to avoid development in hazardous zones and to plan evacuation routes.

• Example need: public safety officials need to plan 

evacuation routes and deliver warnings to communities near volcanoes, along low-lying coastlines vulnerable to tsunamis, next to active faults, and built 

on steep, landslide-prone terrain. 

• Requirements to address the need: thorough characterization of local volcanoes, faults, and unstable 

slopes near vulnerable populations and infrastructure, combined with up-to-date data and models of 

likely flow and wave paths. This information may 

underpin maps, databases, and scenario documents 

that describe evolving hypothetical events.

• New tools to assess the potential for cascading hazards and risks.

• Example need: land-use planners considering building permit applications need to review slope stability 

to make appropriate decisions. More generally, 

stakeholders need to account for the cumulative 

impacts of cascading hazards, such as earthquake 

shaking that destabilizes slopes, which ultimately 

become landslides or submarine sediment flows.

• Requirements to address the need: multidisciplinary 

monitoring systems, integrative computer models to 

anticipate cascading events and the consequences to 

natural and social systems. Science-based scenarios 

may effectively communicate plausible future event 

sequences.

• Geospatial models of permanent, widespread 

land- and sea-level changes that may occur in the 

immediate aftermath of a great subduction zone 

earthquake.

• Example need: emergency managers need to anticipate the effects of submerged and damaged coastal 

roads, rails, pipelines and other infrastructure on 

disaster response and recovery. Sudden land subsidence in excess of meters (several feet) can occur 

after a great subduction zone earthquake, causing 

more widespread tsunami inundation, severe coastal 

erosion, shifting shorelines, and shoaling. 

• Requirements to address the need: predictive 

models of vertical land-level changes and effects 

on the coastal environment during and after big 

earthquakes, updated with land-based and remotely 

sensed geospatial observations. 

• More accurate forecasts of far-reaching hazards to 

avert catastrophes and unnecessary disruptions in 

air and sea transport.

• Example need: air-traffic controllers need to know 

when and how to reroute aircraft during a volcanic 

eruption. Explosive eruptions typical of subduction 

zone volcanoes can send ash clouds miles into the 

atmosphere, potentially invading aviation corridors 

that transport thousands of passengers and millions 

of dollars worth of cargo daily. 

• Requirements to address the need: coupled geologic 

and atmospheric models validated by real-time 

observations (ground-based and remotely sensed); 

interagency collaborations to clearly communicate 

hazards, ensure safe transportation, and minimize 

costly disruptions.

• Information about aftershocks to guide decisions about when and where to re-enter, repair, or 

rebuild buildings and infrastructure after major 

earthquakes.

• Example need: emergency responders need to be 

able to assess the risk to crews working to locate 

survivors in weakened or collapsed buildings. Aftershocks can progressively weaken structures, and 

resulting shaking may be even stronger and more 

locally damaging than the initial event. 

• Requirements to address the need: updated and 

accessible aftershock forecasts informed by multidisciplinary data (for example, satellite imagery, 

seismic and geodetic signals) and underpinned 

by advanced knowledge of the types of earthquakes in subduction zones, regionally specific 

aftershock patterns, and effective strategies for 

risk communication.
Stakeholder Needs 11

Neighborhood-Scale Earthquake Ground Motion Maps

The U.S. Geological Survey (USGS) and 

the University of Washington are working together to produce state-of-the-art 

computer simulations of ground shaking 

from magnitude 9 earthquakes in the 

Pacific Northwest and to assess their 

associated impacts. These efforts are part 

of the M9 Project, funded largely by the 

National Science Foundation, in collaboration with USGS scientists. Because of 

the enormous size of these earthquakes, 

the simulations require supercomputers, 

and to be as realistic as possible they 

use the most accurate available models 

of the Earth and earthquake ruptures. In 

a similar USGS project, in 2007, simulations of all likely, potentially damaging 

earthquakes affecting the City of Seattle 

were used to create urban seismic hazard 

maps, including the one seen at right. 

These maps convey the earthquake shaking expected in Seattle in a user-specified 

time interval. The hazard was mapped at 

a neighborhood scale, which is useful for 

prioritizing retrofitting of Seattle’s oldest and most vulnerable structures, like 

unreinforced masonry buildings, which 

are circled on the map. The maps are 

derived from ground motion simulations 

and show shaking levels that have a 

10 percent likelihood of being exceeded 

(shown in red and yellow shades) within 

a 50-year time period. Shaking in reddish 

and darker brown areas would likely be 

damaging to buildings and infrastructure. 

Shaking strengths are displayed in terms 

useful for structural engineers, as a 

percentage of gravity (where 100 percent 

equals the downward gravitational pull 

of the Earth), from seismic waves with 

1-second period.

PUGET SOUND LAKE

WASHINGTON

LAKE

UNION

GREEN

LAKE

SHIP CANAL

DUWAMISH

WATERWAY

122°25’W 122°20’W

47°30’N

47°35’N

47°40’N

122°15’W

60–80%

60–80%

50–60%

50–60%

40–50%

40–50%

40–50%

40–50%

30–40%

80–110% 20–30%

80–110%

110–145%

110-145%

110–145%

Map from Frankel and others (2007); annotated by J. Gomberg

20

40

60

110

Percent (%)

gravity

Ground shaking strength

High

Low

EXPLANATION

0 1 2 3 MILES

0 1 2 3 KILOMETERS
12 Reducing Risk Where Tectonic Plates Collide—A Plan to Advance Subduction Zone Science

Science Themes of the Subduction 

Zone Science Plan

Theme 1: Advancing Observations and Models 

of Subduction Zone Processes

Information and products that support decisions promoting resilient communities rely on scientific understanding 

of the physical and sociological processes that give rise to 

potentially hazardous events. This section identifies the critical 

observations and research needed to build predictive models of geologic processes in subduction zones. The building 

blocks of these models are described in some detail, ordered 

approximately from the broadest to most focused in scope, 

and are followed by a summary of the key scientific questions, 

investments, and products. The knowledge gained from the 

research activities that underlie these models and from the 

model outputs is needed to make confident estimates of the 

likelihood and impacts of future events, and may translate into 

long-term cost savings by guiding more effective mitigation 

and loss-prevention measures.

A Foundation of Accomplishments and 

Capabilities

USGS scientists and their partners have made pioneering discoveries about subduction zone processes and their 

relations to society and the environment. Discovery about how 

subduction drives great earthquakes, tsunamis, volcanic eruptions, coastal subsidence, and landslides has proceeded at a 

remarkably fast pace, beginning in the 1960s with the recognition of plate tectonics and the origin of subduction zones by 

USGS scientists and their colleagues (Coats, 1962; Plafker, 

1965). Since 2004, USGS geologists have worked with international colleagues to study deposits that recorded land-level 

changes and tsunami inundation following recent great earthquakes in Sumatra, Chile, and Japan, and have learned how to 

recognize similar deposits along U.S. coastlines. USGS and 

Canadian scientists were the first to propose that the Cascadia 

Subduction Zone produces great earthquakes (Heaton and 

Hartzell, 1987; Hyndmann, 1995). Along with Puerto Rican 

and international partners, the USGS has advanced understanding of earthquake and tsunami potential in the northeast 

Caribbean, including the potential for tsunamis to reach the 

Atlantic seaboard (ten Brink and others, 2014). Volcanologists from the USGS and partner universities have successfully forecast volcanic eruptions of Mount St. Helens (1980) 

in Washington State, of Mount Redoubt (1989–90, 2009) and 

Mount Augustine (2006) in Alaska, and of Mount Pinatubo 

(1991) in the Philippines. These forecasts gave emergency 

responders time to evacuate surrounding areas safely and 

reroute aircraft away from hazardous ash clouds, saving thousands of lives and millions of dollars.

Monitoring of subduction zone events and processes 

gives us an unsurpassed ability to accurately recognize 

hazards, produce quantitative hazard assessments, and issue 

timely and appropriate warnings. The USGS maintains 

the Global Seismographic Network in partnership with the 

National Science Foundation (NSF) and the Incorporated 

Research Institutions for Seismology (IRIS) consortium, and 

operates the National Earthquake Information Center, which 

determines and disseminates authoritative products describing 

global earthquakes within minutes of their occurrence. Within 

the United States, the USGS oversees the Advanced National 

Seismic System, which includes regional networks operated 

by university and other government agency partners. Together, 

these seismic networks document where and how often 

earthquakes occur, which allows scientists to investigate how 

earthquake source parameters and geologic setting control 

shaking intensity at the surface, including in subduction zones. 

Data from these seismic networks are key components of the 

National Oceanic and Atmospheric Administration’s (NOAA) 

tsunami warning infrastructure. Geodetic monitoring of 

ground motions conducted by the USGS and its partners has 

revealed slow ground deformation associated with stress accumulation and release during the earthquake cycle, episodically 

creeping faults (see sidebar about tremor and slow slip on 

p. 13), and magma movement beneath volcanoes. The NSF’s 

EarthScope program (http://www.earthscope.org/) has added 

significantly to the Nation’s geodetic monitoring capabilities. 

A growing number of synthetic aperture radar (SAR) satellite constellations operated by international governments and 

private companies, as well as by the U.S. National Aeronautics 

and Space Administration (NASA), will continue to increase 

the frequency with which imagery is available. For instance, 

within the next 5–10 years, new imagery of U.S. volcanoes 

will be available as often as every 4 days.

Monitoring by the USGS and its partners shows that 

volcanoes express unrest in a variety of ways that are diagnostic of their potential for eruption. Monitoring before, during, 

and after the 1980 eruption of Mount St. Helens, for example, 

provided a wealth of close-in observations that have informed 

models of processes preceding, during, and following major 

eruptions. Similarly, landslide monitoring has identified conditions that control initiation and movement, enabling development of regional landslide hazard assessments and forecasts. 

In some cases, monitoring technology developed for one 

hazard has been applied to another, leveraging equipment 

and design. For example, during the 2004–2005 eruption of 

Mount St. Helens, “spider” instruments were first used to 

augment permanent volcano monitoring. These instruments 

may be easily deployed by helicopter-sling operations and 

can collect measurements of earthquake motions, ground and 

glacier movement, rates of lava dome extrusion (eruption), and 

volcanic gas emissions. Following the Oso landslide in 2014, 

the USGS redeployed three spiders to help detect additional 

landslide movement.
Science Themes of the Subduction Zone Science Plan 13

Tremor and Slow Slip Illuminate Potential Earthquake Faults

Analyses of data from global positioning systems (GPS) 

and other geodetic networks have revealed that portions 

of faults sometimes slip slowly, in continuous gradual 

movement for hours to years, without emitting seismic 

waves, and often repeatedly. Although not hazardous 

themselves, slowly slipping fault patches can add stress 

to adjacent stuck (locked) regions of the fault that are 

likely to generate damaging earthquakes. Seismic tremor 

(weak seismic vibrations from swarms of overlapping tiny 

earthquakes) often is a by-product of these slow-slip episodes. Tremor is observed on seismic networks, is more 

easily detected than slow slip, and indicates that slow slip 

is occurring even when not observable directly. Tremor 

and slow slip most often occur in subduction zones, just 

below the locked portions of the plate interface where 

stresses accumulate and are released in great earthquakes. In this example, from south-central Alaska where 

three tectonic plates converge, new tremor observations 

(mostly dark blue patches) span the width of the Yakutat 

Plate (yellow). The termination of tremor at the boundaries of the Yakutat Plate indicates the boundary between 

it and the overriding North American Plate is an active 

fault, capable of generating a very large earthquake. 

Previously, scientists thought that only the Pacific-North 

American Plate boundary (shown as depth contours to 

the top of the subducting Pacific Plate) was active. As 

in many subduction zones, the areas with episodes of 

slow slip (green) occur along the edges of the region that 

slipped in a great earthquake (here, the 1964 M9.2 event, 

whose rupture area is shown in gray). It is still a mystery 

why the areas that have experienced slow slip episodes at 

this location do not coincide with the tremor. Image from 

Wech (2016).

0

153°W 151°W 149°W 147°W

59°N

60°N

61°N

62°N

63°N

64°N

1964

rupture

Slow slip

Tremor 

Yakutat Plate

Anchorage

Prince

William

Sound

Slow slip

Pacific Plate

North 

American 

Plate

EXPLANATION

Tremor rate Increasing

20 km 

40 km 

60 km

80 km

100 km 

Yakutat

North

America

N

Pacific

Plate 

0

0 75 KILOMETERS

75 MILES

Gaps in Knowledge and Capabilities, and 

Scientific Research Frontiers

Characterizing Past Hazardous Events to Forecast the 

Future Using Onshore Clues

Knowledge and capability gap.—Hazard and risk assessments and forecasts invoke the guiding principle that the past 

is a reliable predictor of the future, yet constructing chronologies of past fault slip episodes, volcanic eruptions, tsunamis, 

and landslides remains a major challenge. Chronologies of 

past events must be derived using geologic clues, because 

instrumental records extend back only hundreds of years at 

best—far shorter than the recurrence interval for great subduction zone earthquakes or the eruptive cycles of some volcanoes. Construction of long-term chronologies relies on studies 

of major events recorded in rocks, sediment, and landscapes. 

Linking observations from multiple sites to a single causative 

event relies on the ability to date them sufficiently accurately.

Frontier research—New laboratory approaches and 

facilities, coupled with expanded geologic field studies, will 

constrain event chronologies that are accurate enough to determine whether events on a given fault, volcano, or landslide 

surface are recurring events and thus can be used as guides to 

future events. Targeted geologic field studies in the Nation’s 

subduction zones will collect, analyze, and interpret samples 

using new sediment-core physical scanning methods, highresolution potential-field and seismic imaging, and analyses 

of microfossils. New and refined dating methods and facilities 

will be used.

Refining Subduction Zone Earthquake Chronologies Using 

Offshore Clues

Knowledge and capability gap.—Estimates of the 

recurrence rates of great subduction zone earthquakes differ significantly depending on whether they are derived from 

offshore or onshore geologic studies. In some places, rates are 

unknown. It is especially important to resolve the differences 
14 Reducing Risk Where Tectonic Plates Collide—A Plan to Advance Subduction Zone Science

in recurrence rates of Cascadia earthquakes having M8–9 

that are inferred from studies of submarine sediment and mud 

flow deposits (turbidites) with those based on measurements 

of coastal uplift and subsidence from marsh stratigraphy and 

tsunami deposits (see sidebar on next page about records of 

earthquakes). These different measurement methods translate 

to long-term-average ground shaking estimates that differ by 

40 percent, which affects many parameters used for earthquake planning, such as seismic building design criteria.

Frontier research.—Acquisition and analyses of offshore 

sediment cores and high-resolution subsurface and bathymetric imagery will provide means of testing conditions under 

which turbidites may be generated by great earthquakes. 

Earthquake chronologies from offshore sediment cores may be 

compared with those from onshore studies of coastal landlevel changes and tsunami deposition, earthquake-triggered 

landslides, and geodetic and ground motion modeling.

Understanding Cycles of Volcanic Eruptions

Knowledge and capability gap.—Volcanoes have diverse 

eruptive styles and rates that challenge forecasts and evaluations of future activity. All volcanoes studied to date appear to 

have periods of frequent eruptions separated by longer quiet 

intervals, but the length of active and quiet periods vary from 

one volcano to another: active periods may last anywhere from 

a few years to centuries, and quiet periods may range from 

a few decades to thousands of years. Most subduction zone 

volcanoes erupt infrequently, so collecting interpretable monitoring data that span the full eruption cycle, from quiescence 

to the buildup to eruption, requires adequately instrumenting 

many potentially hazardous volcanoes.

Frontier research.—Studies that systematically sample 

volcanic rocks, lavas, and gasses and apply state-of-the art 

age-dating methods improve knowledge of eruption chronologies and reveal the causes and characteristics of eruption 

clustering. Improving eruption chronologies, in turn, improves 

the confidence and accuracy of volcano hazard assessments at 

high-threat volcanoes.

Forecasting Destructive Earthquake-Triggered Landslides 

Knowledge and capability gap.—Hazard assessments for 

earthquake-shaking triggered landslides are based on highly 

simplified models and incomplete input data, and generally 

do not provide estimates of the areas likely to be covered 

by landslide debris; oftentimes areas forecasted to fail are 

over-estimated by more than a factor of two; and landslides 

frequently occur in locations forecast as stable.

Frontier research.—Laboratory analyses of field samples 

from landslide-susceptible slopes will help identify conditions 

affecting potential slope failure during earthquake shaking. 

These analyses are used to constrain models of how seismic 

energy is amplified along hillslopes for the range of sizes 

and types of subduction zone earthquakes. The model results 

help characterize the response of shallow Earth materials to 

shaking, show how the materials change as they slide, and 

elucidate the role of saturated soils in controlling the initiation, mobility, and run-out distance of earthquake-triggered 

landslides.

Anticipating Great Subduction Zone Earthquakes and 

Tsunamis Using Seafloor Observations

Knowledge and capability gap.—The paucity of seafloor sensors limits our ability to accurately anticipate where 

subduction zone earthquakes will happen, the severity of 

their shaking, and their propensity to generate tsunamis. The 

destructive potential of ground shaking during great subduction zone earthquakes depends crucially on the earthquake 

depth and the geometry of the tectonic plate interface (essentially giant faults), as well as on the location of locked sections of the plate interface relative to populations and critical 

infrastructure. Significant areas of these interfaces lie beneath 

the ocean, where we have few or no observations to accurately 

determine their configurations and whether they are locked 

or not.

Frontier research.—Repeat temporary deployments of 

seafloor seismic, geodetic and other instruments provide firstorder constraints on key unknown attributes of plate interfaces. 

Seafloor observatories operated by the Japanese government, 

for example, have demonstrated the practicality and value of 

seafloor monitoring, which illuminates the geometry, depth, 

and spatially variable strength of subduction zone faults. Such 

information leads to reduced uncertainty regarding where and 

why some regions of plate interfaces are stuck while others 

slide freely (see sidebar about seafloor instrumentation on 

p. 16). Knowledge of the temporal and spatial variability 

in interface behavior requires that such instrumentation be 

deployed permanently and record continuously. Offshore sensors must transmit data from the seafloor in real time in order 

to be useful for detection of activity that may be precursory to 

a major earthquake and tsunami, and to improve warnings of 

earthquake shaking and tsunami waves.

Determining the Role of Water in Subduction Zone 

Processes

Knowledge and capabilities gap.—Water plays a key 

but poorly understood role in determining where faults are 

stuck and ultimately slip in earthquakes, and where they slip 

slowly without radiating damaging seismic waves. Water also 

promotes magma generation below subduction zone volcanoes 

and controls eruption style and energetics. Water is thought to 

be trapped in sediments and minerals and transported to great 

depth during subduction, where it is released due to intense 

pressures and temperatures. At the land surface, elevated pore 

pressure from infiltrated rainfall and snowmelt affects slope 

stability and therefore landslide probabilities. The accuracy of 

earthquake, landslide, and eruption forecasts would be greatly 

improved by increased understanding of water entrainment 
Science Themes of the Subduction Zone Science Plan 15

The Onshore and Offshore Records of Great Earthquakes

Scientists use reconstructed histories of past great earthquakes 

to estimate the likelihood of future events and their effects. The 

Cascadia earthquake chronologies estimated from onshore and 

offshore studies differ, leading to significant uncertainties in 

seismic hazard (ground shaking) assessments. Some estimates of earthquake repeat times differ by hundreds of 

years, which translates into ground shaking intensities 

that differ by about 40 percent; such differences have 

major effects on building codes and construction 

costs. Preserved onshore coastal deposits left by 

tsunami waves and sudden subsidence record a 

long-term history of large earthquakes, evident 

as abrupt changes in the subsurface layers 

in sediment cores. The photograph shows 

a core collected in Grays Harbor, Washington, after the core was split open. The 

abrupt color change in the core indicates 

that ancient tidal marshes, where peat 

and mud developed (the reddish-brown 

sediment), were suddenly inundated with 

sands and muds (grayish sediment)—

most likely due to subsidence during a 

great Cascadia earthquake. Analyses 

of preserved microscopic organisms 

above and below this abrupt change in 

the core (the photo-micrograph shown 

in the top left image) and knowledge of 

their preferred habitat provide estimates 

of the amount of subsidence, which helps 

constrain the magnitude of the causative 

earthquake (images from Phipps and 

others, 2015). Offshore, strong earthquake 

shaking along steep submarine slopes 

may loosen massive volumes of sediments, mixing with water to become slurries that rush downslope along seafloor 

canyons. These turbidity currents leave 

deposits called turbidites, which are 

identifiable in sediment cores collected 

far offshore on the continental slope and 

deep seafloor. High-resolution maps of 

seafloor topography offshore Washington 

State (map modified from Goldfinger and 

others, 2016) show inferred flow channels 

that turbidity currents might follow (teal 

lines). By correlating similar turbidite characteristics among selected cores across the region (red dots 

show core locations), scientists have estimated the dates and magnitudes of 

large prehistoric great earthquakes. USGS scientists and university colleagues are working to 

understand the different onshore and offshore estimates of Cascadia earthquake recurrence. 10 centimeters

Peaty mud

Sandy and mud

Microscopic diatoms Up

Modified from Phipps and others, 2015

10 micrometers

48°N

126°W

Map modified from Goldfinger 

and others, 2016

0 10 20 KILOMETERS

0 10 20 MILES

Juan de Fuca Canyon

Nitinat Canyon

Barkley Canyon

WASHINGTON

Grays Harbor
16 Reducing Risk Where Tectonic Plates Collide—A Plan to Advance Subduction Zone Science

Seafloor Instrumentation and the 2011 Magnitude 9.0 Tōhoku, Japan, Earthquake

Following the 2011 magnitude (M) 9.0 Tōhoku, Japan, 

earthquake, scientists made important discoveries about 

the earthquake and tsunami because they had already 

mapped the topography of the seafloor (bathymetry), 

seismically imaged geologic units below the seafloor, and 

installed seafloor monitoring instruments. Continuous 

records of changes in the seafloor elevation and height of 

the water column (measured by the pressure it exerts on 

the seafloor), confirmed that the plate interface slipped 

slowly (left figure, pink area; map modified from Ito and 

others, 2013) during the two-day foreshock sequence prior 

to the M9.0 event (black star marks earthquake epicenter). 

Seafloor pressure records during the M9.0 earthquake, as 

well as measurements of seafloor position using acoustically linked global positioning system (GPS) receivers 

(blue symbols labeled “GPS/A”) documented an enormous 

amount of fault slip (more than 50 meters, or 64 feet) in the 

shallowest part of the fault (Iinuma and others, 2012). Highresolution marine seismic-reflection images (right figure, 

from Kodaira and others, 2012)—effectively like sonograms 

of the subsurface—revealed that the M9.0 earthquake 

dramatically deformed sediments (especially within yellow 

circles; note how continuous layers in the “Before” image 

appear mangled in the “After” image). These large disturbances of the seafloor and the sediments and rocks along 

the fault accounted for the tremendous ensuing tsunami, 

and the potential for similarly large future events are now 

being included in tsunami inundation models worldwide. 

Moreover, comparison surveys of seafloor topography 

before and after the 2011 earthquake (see, for example, the 

green line in the “After” image that shows the pre-event 

topography) revealed evidence of a submarine landslide 

that may have intensified the tsunami (Tappin and others, 

2014). Seafloor measurements over the nine years prior to 

the 2011 M9.0 earthquake led to more accurate estimates of 

how stresses are accumulating on the plate interface than 

can be obtained from land-based GPS data alone (yellow 

symbols on map; Sato and others, 2013).

141 ̊E 144 ̊E

37 ̊N

40 ̊N

Trench

3/11

M 9.0

Slow

 slip

JAPAN

Map modified from Ito and others, 2013

PACIFIC

OCEAN

0 10 20 KILOMETERS

0 10 20 MILES

Land-based GPS stations

GPS/A

Pressure sensor

Seismic reflection imagery

EXPLANATION

1 KILOMETER

Before earthquake

After earthquake 1 KILOMETER

1 KILOMETER

1 KILOMETER
Science Themes of the Subduction Zone Science Plan 17

and release, and how it controls the occurrence of these 

hazardous events.

Frontier research.—Advanced laboratory techniques that 

precisely measure water and other constituents of rocks that 

were transported to the surface by geologic processes, and 

new field techniques that accurately detect and measure gases 

emitted from active volcanoes provide key constraints on the 

conditions required to trap and release water. These measurements, coupled with new computer models, seismological 

and geodetic analyses, and laboratory studies will lead to new 

insights into the mechanical and chemical effects of fluids in 

landslides, faulting, and volcanism.

Addressing Multidisciplinary Questions About Sediment 

Transport

Knowledge and capabilities gap.—Sediment discharged 

from the small, high-sediment-yield watersheds typical of 

subduction zones is eventually deposited in the deepest seafloor basins and represents the majority of sediment reaching 

the world’s oceans. This sediment plays a key role in subduction zone geologic processes, yet the interactions among the 

many natural systems that affect and are affected by sediment 

transport processes are poorly constrained. For example, 

earthquake-generated land-level changes undoubtedly alter the 

paths of sediment-laden streams and rivers and thereby modify 

flooding hazards and ecosystem habitats, but the models do 

not exist to predict the magnitude and precise nature of these 

changes.

Frontier research.—Questions about sediment transport 

and subduction zone processes are best addressed by collaborations amongst hydrologists, oceanographers, and geologists across USGS programs. For subduction zone hazard 

assessments, scientists supported by the Natural Hazards 

Mission Area study how sediment transport affects coastal 

erosion, submarine landslides, and the creation of seafloor 

turbidite deposits from which dates and magnitudes of past 

strong earthquakes can be deduced. Scientists supported by 

the Climate and Land Use Change and Water Mission Areas, 

as well as the Pacific Coastal and Marine Science Center, are 

addressing complementary questions about sediment transport; 

for example, geologic trenching and landscape studies examine the deposition and erosion associated with past extreme 

storms, sea level changes, or dam construction.

Mapping Bathymetry and Topography from the Deepest 

Seafloor to Continental Interiors

Knowledge and capabilities gap.—In subduction zones, 

high-resolution, regional, cross-shoreline topographic data 

have numerous applications, yet are lacking in many places. 

Bathymetric and topographic data are the foundation of products like assessments of inundation and earthquake hazards, 

geologic maps, and comprehensive sediment transport models. 

For example, cross-shoreline topographic data are needed 

to determine if faults mapped onshore to the coast extend 

offshore, and to constrain models of tsunami impacts, which 

depend strongly on the topography offshore and onshore. In 

addition to addressing geologic needs, such data also contribute to understanding of forest wetland ecology, benthic habitat 

structure, and ecosystem interactions (for example, the high 

topography built by subduction zone processes can create rain 

shadows and deserts).

Frontier research.—Data collection designed and 

accomplished through collaborations among the many users 

of topographic data will most effectively address all their 

needs. Such an effort will build on the USGS Coastal National 

Elevation Database Project (CoNED; http://topotools.cr.usgs.

gov/coned/index.php), which is creating seamless elevation 

models for the U.S. coastal zone in collaboration with the 

USGS’s National Geospatial and 3-D Elevation (3DEP) and 

Coastal and Marine Geology Programs, the U.S. Army Corps 

of Engineers, and NOAA.

Key Questions, Investments, and Products

This theme, “Advancing Observations and Models of 

Subduction Zone Processes,” addresses fundamental science 

questions using predictive models. The following list summarizes the previous section, noting the outstanding gaps recast 

as science questions, the investments needed to make major 

leaps forward toward answers to them, and potential products 

that an enacted Subduction Zone Science Plan could deliver. 

The relevant products in table 1 and investments in its accompanying list are noted in abbreviated form.

1. How well do past events foretell the future? This question summarizes the gaps and investments needed to 

characterize past subduction zone events. For earthquakes, chronologies of past events will reveal whether 

characteristics of large hazardous earthquakes may be 

accurately anticipated from studies of more frequent 

smaller earthquakes. For landslides, chronologies 

coupled with knowledge of historic and paleo-climatic 

conditions and regional geology will answer questions 

about what initiates slippage of landslide masses. For 

volcanoes, chronologies of eruptions from volcanoes in 

different settings will show what, if any, predictable patterns in eruptive behaviors exist and how those patterns 

vary among volcanoes. 

 Investments: offshore sediment-core samples, 

images of subsurface geologic structures, temporary 

geophysical deployments; high-resolution multibeam 

bathymetry offshore, airborne and space-based topographic imagery onshore; expanded geologic field 

programs; and laboratory capabilities for dating and 

analyzing the physical properties of rock samples 

(D, E, G, H in table 1’s list).
18 Reducing Risk Where Tectonic Plates Collide—A Plan to Advance Subduction Zone Science

 Products: Hazard and risk assessments, scenarios, 

forecasts (table 1).

2. Are M8–9 earthquakes preceded by precursory processes (such as foreshocks or slow fault slip)?

 Investments: denser onshore seismic and geodetic 

monitoring; permanent and temporary seafloor 

seismic and geodetic monitoring instrumentation; 

and offshore sediment-core samples, images of subsurface geologic structures, temporary geophysical 

deployments (A–D in table 1’s list). 

 Products: hazard and risk assessments, warning 

systems, new types of forecasts (table 1).

3. What processes generate and consume water during subduction, and how does water control magma generation, 

fault movements, and landslides? 

 Investments: denser onshore seismic and geodetic 

monitoring; permanent seafloor seismic and geodetic 

monitoring instrumentation; offshore sediment-core 

samples, images of subsurface geologic structures, 

temporary geophysical deployments; geologic field 

programs and laboratory capabilities for dating and 

analyzing the physical properties of rock samples 

(A, C, D, G, H in table 1’s list). 

 Products: high-resolution hazard and risk assessments, cascading event assessments (table 1). 

4. How are sediments redistributed from their source on 

land to the seafloor? 

 Investments: offshore sediment-core samples; 

images of subsurface geologic structures, temporary 

geophysical deployments; high-resolution, multibeam bathymetry offshore, adjacent to airborne and 

space-based topographic imagery onshore; geologic 

field programs; multidisciplinary models of geologic 

and sediment transport processes (D, E, G, and I in 

table 1’s list). 

 Products: assessments of cascading subduction zone 

events (table 1), new knowledge of how sediments 

are redistributed from continental interior to the deep 

seafloor. 

Theme 2: Quantifying Natural Hazards and Risk

Natural hazard assessments are estimates of the characteristics of a given event type (for example, past rates of 

occurrence, future probability, magnitude, duration, speed of 

onset, and spatial extent) and are typically either scenariobased or probabilistic. Scenario-based assessments seek to 

estimate the impact of a specific hypothetical natural event, 

constrained by historical information, by geologic field and 

laboratory data, or by deterministic computer modeling. 

Probabilistic hazard assessments combine multiple scenarios 

with information about recurrence times of hazardous events. 

They convey probabilities of experiencing certain levels of 

effects over a specified period of time by accounting for the 

likelihoods of all the scenarios. This section considers both 

types of assessments: both are needed for planning for natural 

hazards over time scales of years to decades.

Risk is the likelihood that a natural hazard event or 

events will cause a human, economic, or ecosystem loss and is 

calculated by combining the hazard probability with exposure 

and vulnerability of populations, economies, infrastructure, 

and ecosystems. Estimating risk requires a multidisciplinary 

approach, involving both scientific data and methods developed in social and behavioral sciences, as well as collaborations with engineers, land-use planners, and insurance entities. 

The knowledge and capabilities gaps and frontier research 

areas identified in this theme address not only the potential 

for a particular subduction zone event to occur, but also how 

that event may affect subsequent natural events, the built 

environment, or human activities. These are ordered roughly 

from the broadest to most focused in scope, and are followed 

by a summary of the key outstanding questions, investments 

and products.

A Foundation of Accomplishments and 

Capabilities

The USGS produces probabilistic earthquake groundshaking hazard assessments for the Nation, including our subduction zones, in the National Seismic Hazard Maps (NSHM; 

available at https://earthquake.usgs.gov/hazards/hazmaps/). 

These maps are the basis for the seismic codes for buildings, 

highway bridges, landfills, dams, and other infrastructure. 

These earthquake hazard assessments incorporate the best 

data available about fault characteristics that can be inferred 

from chronologies of past earthquakes and tsunamis recorded 

in geologic, historic, and instrumental data. Higher-resolution 

maps that account for the complex three-dimensional effects 

that local geologic structures have on ground shaking exist for 

several urban areas (see sidebar on about neighborhood-scale 

maps p. 11). The USGS is also a leader in the computer simulation of earthquake ground motions for a variety of plausible 

earthquake models, particularly those in subduction zones.

USGS scenario ground-shaking maps (called “ShakeMaps;” https://earthquake.usgs.gov/earthquakes/shakemap/) 

serve as input to the FEMA Hazus vulnerability and risk 

assessment tool (available at https://www.fema.gov/hazus) 

and, together, ShakeMaps and Hazus are key resources for 

emergency management, loss estimation, and emergency 

response exercises. For example, ShakeMaps for 20 hypothetical earthquakes provide the foundation for a scenario catalog 

hosted by the Washington State Emergency Management 
Science Themes of the Subduction Zone Science Plan 19

Division and Department of Natural Resources to assist 

cities and counties in their mitigation plan development 

(https://fortress.wa.gov/dnr/protectiongis/seismicscenarios/). 

ShakeMaps for great subduction zone earthquakes were 

input to Hazus to serve as the foundation of the Oregon 

Resilience Plan (https://www.oregon.gov/OMD/OEM/

Pages/osspac/osspac.aspx#Oregon_Resilience_Plan)

and the 2014 and 2016 FEMA-led Alaska Shield 

(https://www.fema.gov/media-library/assets/videos/93182) 

and Cascadia Rising (https://www.fema.gov/media-library/

assets/documents/116120) national level exercises, which test 

the effectiveness of response and recovery within Federal, 

State, and local governments, and private entities individually 

and collectively.

The USGS has released hazards information for every 

high-threat subduction zone volcano in the Nation. For many 

of the volcanoes posing the greatest threat, the USGS has 

mapped the potential for ground-based volcanic impacts—

lava, mud and pyroclastic flows, avalanches, and landslides—

and more far-reaching hazards such as volcanic gases and ash 

falls. Long-term assessments are based upon detailed geologic 

mapping and dating of volcanic deposits, which provide a 

record of past eruptions, integrated with high-resolution topographic mapping and computer models to forecast the effects 

of these eruptions.

The USGS National Volcano Early Warning System 

(NVEWS, https://volcanoes.usgs.gov/vhp/nvews.html) is a 

proposed national-scale system to assess the threat posed by 

each volcano in the Nation, to prioritize study and monitoring of volcanoes according to their risk, with the primary 

goal of providing timely warning of an eruption to potentially 

affected areas and communities. U.S. volcanoes have been 

grouped into five threat categories (very high, high, moderate, low, and very low) based on a combination of volcanic 

hazards and exposure of population and property. The 2005 

NVEWS assessment of volcanic threat and level of instrumentation identified 37 volcanoes in Alaska and the Mariana 

Islands that have either inadequate or no monitoring networks in place, and 21 additional volcanoes that have some 

deficiencies in their monitoring (Ewert and others, 2005). 

Since the 2005 report, progress towards NVEWS’s goals has 

included instrumentation upgrades on six volcanoes, design 

and permitting of comprehensive networks for three volcanoes, upgrading of data telemetry from analog to digital where 

feasible, development and installation of infrasound (acoustic) 

monitoring instruments in Alaska and the Pacific Northwest, 

and repair of numerous failed remote instruments in Alaska. 

Together, USGS scientists and stakeholders have developed 

volcano emergency response plans at more than 88 volcanoes 

nationwide.

USGS scientists have identified conditions that facilitate 

landslides triggered by rainfall and earthquakes and have 

developed multiple approaches to regional mapping to depict 

landslide-prone areas. Some of these approaches have been 

developed for and applied to earthquake- and rainfall-induced 

landslides in Oregon, Washington, and Alaska. Subductionzone-related uplift, the inevitability of future earthquakes, and 

wet winter climates make large parts of these States highly 

susceptible to landslides. For example, the USGS has produced maps that show where landslides are likely to initiate in 

Seattle, Washington (fig. 2).

USGS scientists have developed a probabilistic tsunami 

hazard assessment (PTHA) framework that has been used in 

engineering and flood insurance applications, following the 

same probabilistic approach that underlies the National Seismic Hazard Maps. Unlike the seismic hazard maps, though, 

the tsunami hazard assessment has the added challenge of 

needing to include probable earthquake sources throughout 

the ocean basins, because tsunami amplitude attenuates much 

more gradually with distance than earthquake-induced ground 

shaking. Products from PTHA range from estimates of tsunami runup (the highest elevation a tsunami reaches on land) 

WASHINGTON

OREGON

Seattle

PUGET

SOUND

N

EXPLANATION

Shallow landslide

Landslide susceptibility

High

Moderate

Low

0 0.5

0 0.5 1 KILOMETER

1 MILE

Figure 2. Example of a landslide susceptibility map after a 

period of heavy rainfall (2 inches, or 52 millimeters, in 1.5 days). 

This assessment, along a key railroad corridor about 9 miles 

(15 kilometers) north of Seattle, Washington, shows which areas 

would be most susceptible to shallow landslides (purple areas 

have high susceptibility). From Godt and others (2008).
20 Reducing Risk Where Tectonic Plates Collide—A Plan to Advance Subduction Zone Science

2

3

4

5

6

8 7

9

10

4

2

3

2

2

4

4

2

6

5 6

7

7

6

5

2 4

6

6

9

6

7

6

3 6

3

6

5

9

7

2

10

6

7

9

2

3

3

3

5

9

9

2

4

2

5

4

6

3

4

5

6

8

5

5

7

3

3

4

5

6

6

8

4

4

6

4

5

6

3

8

9

10

45°59’N

46°N

46°01’N

123°57’W 123°56’W 123°55’W

EXPLANATION

0.5 to 2.0

2.1 to 4.0

4.1 to 6.0

6.1 to 8.0

8.1 to 10.0

Tsunami wave height 

(meters)

0 0.5

0 0.5 1 KILOMETER

1 MILE

Seaside, Oregon

Figure 3. Tsunami wave height estimates for Seaside, Oregon, calculated for a range of likely 

earthquake sources of magnitude 8–9. Contours are drawn at 1 meter (~3 feet) intervals. At the beach, 

for example, waves could be 8, 9, or 10 meters tall (red contours), while the more inland parts of town 

might see waves of 2, 3, or 4 meters (light blue contours). These wave height estimates are used for 

conservative, long-term planning and design. Land areas in white and the Pacific Ocean in blue; roads 

are thin gray lines. Image modified from Tsunami Pilot Study Working Group, 2006.
Science Themes of the Subduction Zone Science Plan 21

to probabilistic inundation maps that show how far inland a 

tsunami is likely to reach at a particular coastal location. A 

variety of PTHA products have been created for a pilot project 

involving USGS, NOAA, and FEMA to update FEMA’s 

Flood Hazard Maps in Seaside, Oregon; an example is shown 

in figure 3. With support from the U.S. Nuclear Regulatory 

Commission, the USGS also completed an assessment of 

the tsunami hazard along the U.S. East Coast (ten Brink and 

others, 2014).

USGS researchers have used population characteristics 

within tsunami hazard zones to improve tsunami evacuation 

protocols in coastal communities. These studies take into 

account tourist and non-residential populations who may be 

more vulnerable because of a lack of situational awareness 

during a hazardous event, as well as populations with limited 

mobility or health issues who might be unable to evacuate without assistance. Using these analyses, for example, 

researchers determined pedestrian evacuation times within the 

Cascadia Subduction Zone (Wood and others, 2016). 

Gaps in Knowledge and Capabilities and 

Frontiers of Scientific Research

Communicating Hazard and Risk to Communities

Knowledge and capabilities gap.—There is a dearth of 

knowledge about how to best tailor hazard communications to 

target diverse at-risk communities. While USGS researchers 

have studied vulnerable populations (Wood and others, 2016), 

little is known about how historical, cultural, and economic 

factors may influence the ability or willingness of a population 

to utilize USGS tools to prepare for, respond to, and recover 

from a hazardous event.

Frontier research.—USGS scientists will seek collaborations with behavioral psychologists, sociologists, user-centered 

designers, communications experts, and other Federal, State, 

and local agencies to understand when and how to release 

information in order to ensure effective and appropriate 

response. Such research is especially important for implementing new warning systems and in communicating preparedness 

messages that help subduction zone residents to prepare for 

and react to a complex cascade of events and consequences 

following a major earthquake, tsunami, widespread landslides, 

or a volcanic eruption.

Discriminating Between Causes and Effects of 

Subduction Zone Processes and Climate Change

Knowledge and capabilities gap.—Subduction zone 

science relies on understanding climate change, because 

short-term events that occur in subduction zones can affect, 

or be affected by, longer-term climate changes. These interactions have been quantified poorly at best, but examples of 

some qualitatively understood interactions include climatechange-driven sea-level rise that affects the extent of seawater 

inundation by tsunamis and by earthquake-induced coastal 

subsidence; changes in rainfall and the thinning and retreat 

of tidewater glaciers that affect submarine and subaerial 

landslide susceptibility, size, and frequency; and ash clouds 

from large volcanic eruptions that temporarily alter the rate 

of average global temperature rise. These interactions need to 

be considered not only through the science underlying hazard 

assessments, but also to assess the exposure, vulnerability, and 

risk from both subduction zone and climate-change processes 

(which is a goal also noted explicitly in the USGS Climate and 

Land Use Change Science Strategy).

Frontier research.—Accurate interpretation of both the 

geologic record of subduction zone processes and of climate 

change requires forefront studies of the interplay between 

them, which will improve interpretations of geologic evidence 

of past subduction zone events and forecasts of future ones. 

Studies of tsunami inundation and the deposits they leave 

in the geologic record, earthquake-generated coastal landlevel changes, and landslide occurrence in areas affected by 

sea-level and glacial changes will engage scientists from the 

USGS Climate and Land Use Change Mission Area, the Natural Hazards Mission Area, the National Cooperative Geologic 

Mapping Program, and partners at State geological surveys.

Assessing the Nation’s Energy and Mineral Resources

Knowledge and capabilities gap.—The economic 

consequences of steady geologic processes and of damaging 

events in subduction zones have only begun to be quantified. 

The former produce geothermal energy and mineral resources, 

but latter may disrupt their production. The abundant volcanism along subduction zones makes geothermal energy a 

A technician installs lahar monitoring equipment in 

Washington State. U.S. Geological Survey photograph 

by Elizabeth Faust.
22 Reducing Risk Where Tectonic Plates Collide—A Plan to Advance Subduction Zone Science

key resource in global subduction zones (for example, in the 

Republics of the Philippines and Indonesia, Japan, and New 

Zealand). The majority of the world’s copper is produced from 

shallow granitic intrusions that formed beneath subduction 

zone volcanoes, and gold, silver, tungsten, and tin may form as 

direct mineral deposits in subduction settings. A preliminary 

USGS study (Menzie and others, 2011) provides an example 

of the effects of a great subduction zone earthquake on the 

availability of mineral resources; in this study USGS scientists concluded that the 2011 M9.0 Tōhoku, Japan, earthquake 

and tsunami disrupted Japan’s mineral and mining industries, 

which supply the world with 25 percent of its iodine, 10 percent of its titanium, and smaller but significant fractions of 

other nonfuel minerals. 

Frontier research.—Advanced USGS subduction zone 

science will focus on both the economic benefits and the 

hazards of subduction zone processes, particularly geothermal 

power and mineral assessments. USGS studies of the geothermal potential of the Cascades volcanoes indicate their potential is relatively modest (Guffanti and Muffler, 1995; Muffler 

and Temanyu, 1995), but many Alaskan volcanoes erupt 

more frequently and may have greater geothermal potential 

(for example, Makushin Volcano, Akutan Peak, Mount Spurr, 

Augustine Volcano, Mount Okmok, and Korovin Volcano). 

Studies of subduction zone processes also may address the 

energy-producing potential of volcanic sources, their effects 

on mineral resources, and the potential of subduction zone 

events to disrupt supply chains that depend on energy and 

mineral resources from subduction zones.

Assessing the Potential for Submarine Landslides

Knowledge and capabilities gap.—The ability to assess 

the potential for submarine landslide occurrence is almost 

entirely lacking, even though such slides may generate locally 

hazardous tsunamis and can damage offshore infrastructure 

(see sidebar on next page about using bathymetric data to 

identify tsunami hazards). It is unknown if existing slope stability models, developed for terrestrial landslides, can be used 

for submarine slopes, given the significant differences in sediment mechanical properties and hydrodynamics of sediment/

fluid mixtures between onshore and offshore environments. 

Existing bathymetric data lack adequate resolution and submarine slope materials are sparsely sampled in most regions.

Frontier research.—Collection of samples of slope 

materials and high-resolution bathymetric data, determination 

of ages and stability-affecting properties, and development of 

physical models at a regional scale will identify the distribution and characteristics of submarine landslides. Results from 

these activities can help determine the applicability of existing 

slope-stability models and contribute to new ones as needed.

Accounting for Locally Hazardous Tsunamis

Knowledge and capabilities gap.—Probabilistic tsunami 

hazard assessments consider only earthquakes that occur on 

the plate interface, neglecting tsunami-generating landslides, 

volcanic events, and earthquakes on shallow intraplate faults, 

particularly those close to shore (which may locally be more 

hazardous than trans-oceanic tsunamis). For example, of the 

tsunami-related losses that followed the 1964 M9.2 1964 

Alaska earthquake, most of the damage and 76 percent of the 

fatalities were generated by localized, subaerial and submarine landslides (Suleimani and others, 2009). Ninety tsunamis 

of volcanic origin have been produced in the world’s ocean 

basins in the past 250 years (Beget, 2000), but the majority 

of submarine volcanism occurs undetected. Information is 

lacking about the frequencies of submarine volcanic activity, offshore landslides, shallow intraplate fault earthquakes, 

and about how these events displace seawater to generate 

tsunami waves (see sidebar about using bathymetric data to 

identify tsunami hazards on next page). 

Frontier research.—Understanding frequencies and 

mechanisms of submarine volcanic activity, offshore landslides, shallow intra-plate fault earthquakes, and how these 

events displace sea water to generate tsunami waves relies on 

the development of new instruments that can make long-term 

measurements on the seafloor. Accurately measuring slow 

displacements and earthquakes (with geodetic and seismic 

sensors), and volcanic activity (with hydro-acoustic arrays), in 

concert with acquisition of seafloor bathymetry data and other 

types of imagery, would reduce the uncertainty in estimates of 

shallow, intraplate slip rates and will identify potential submarine landslides and volcanic sources.

Predicting How the Built Environment Will Respond to 

Strong Earthquake Shaking

Knowledge and capabilities gap.—The duration and 

oscillation periods of shaking resulting from great (M>8) 

subduction zone earthquakes are significantly longer than for 

other types of earthquakes—and can be particularly damaging 

to tall buildings and other large structures—but these factors 

are not accounted for in most earthquake risk assessments and 

structural design codes. Both computer simulations of time 

variations in ground motion and empirical characterizations 

(such as ground-motion prediction equations) are needed so 

that scientists and stakeholders can accurately predict the 

shaking created by great earthquakes. These simulations and 

empirical characterizations are particularly important because 

they include the seismic amplification by the sedimentary 

basins that underlie cities like Seattle and Tacoma, Washington, Portland, Oregon, and Anchorage, Alaska. These products 

may be combined with exposure (for example, building inventories) and fragility data for risk modeling.
Science Themes of the Subduction Zone Science Plan 23

Using Bathymetric and Topographic Data to Identify Local Tsunami Hazards

In March 1964, a tsunami engulfed Chenega, a small fishing village on Chenega Island in Prince William Sound, 

Alaska, killing 23 people and a significant fraction of 

the fish population. Recently acquired high-resolution, 

shaded-relief bathymetric and topographic images reveal 

the probable cause of the tsunami: failure of the steep 

submarine slopes bordering the coastline was initiated by 

the magnitude 9.2 Alaska earthquake that occurred the 

same day, spawning massive sediment flows and tsunami waves. Many of the other destructive tsunamis that 

followed this earthquake were likely caused by similar 

submarine landslides. Data like these help scientists 

understand the sources of these local tsunamis so that the 

impacts of future events may be mitigated.

Map modified from Brothers and others, 2016 0 750 1,500 METERS

0 2,500 5,000 FEET

Water depth (meters)

25

255

485

EXPLANATION

Failed steep sediment slopes

tsunami inundation

Chenega

Village

Landslide flow paths

N

Frontier research.—New collaborative studies that 

engage both engineers and scientists will employ recorded 

and simulated ground motions to assess the vulnerabilities of 

the built environment to strong shaking from great subduction zone earthquakes at the neighborhood scale. Simulations 

would benefit from investments in high-performance computing tools, development of observationally constrained threedimensional models of the subsurface, and validation against 

earthquake ground motions recorded during large earthquakes.

Key Questions, Investments, and Products

The questions below summarize the outstanding gaps in 

knowledge and capabilities relevant to theme 2 of this Subduction Zone Science Plan, “Quantifying Natural Hazards and 

Risk,” the investments needed to make major progress towards 

answering them, and potential products that an enacted plan 

could deliver. The investments and products are noted in 

abbreviated format and by reference to table 1 (on p. 2).

1. How do subduction zone events affect climate and 

vice versa? 

 Investments: geologic field programs that constrain 

land- and sea-level changes on timescales of millennia and those caused by major instantaneous events; 

multidisciplinary models that include simulation 

of both climatic and geologic processes (G and I in 

table 1’s list).

 Products: high-resolution hazard and risk assessments; models of cascading events (table 1); climate 

change assessments that more accurately account for 

feedbacks between geologic and climatic processes.
24 Reducing Risk Where Tectonic Plates Collide—A Plan to Advance Subduction Zone Science

2. How do long-term processes and major events in a subduction zone affect energy and mineral resource distributions and supplies? 

 Investments: three-dimensional subsurface models 

of processes affecting mineral and gas deposits; geologic field mapping, coring and subsurface imaging 

programs; laboratory capabilities; multidisciplinary 

models (F, G, H, I in table 1’s list); and assessments 

of the impacts of subduction zone hazards and 

risks on geothermal power production and mineral 

resources.

 Products: high-resolution hazard and risk maps, 

databases, and tables conveying information about 

the distributions of faults, heat flow, rocks, fluids 

and other parameters relevant to energy and mineral 

resources; assessments of the probabilities of cascading geologic events (table 1), and their effects on 

the potential and resilience of geothermal power and 

mineral resource production.

3. What are the hazards and risks from submarine 

landslides? 

 Investments: multidisciplinary (for example, seismic 

and geodetic) onshore and offshore monitoring; offshore sediment-core samples, images of subsurface 

geologic structures, temporary geophysical deployments; high-resolution, multibeam bathymetry 

offshore, adjacent to airborne and space-based topographic imagery onshore; laboratory capabilities for 

dating and analyzing physical properties of rock and 

sediment samples (B, C, D, E, H in table 1’s list). 

 Products: high-resolution hazard and risk assessments and event scenarios extending from offshore 

to the continental interior (table 1). 

4. What are the hazards and risks from locally generated 

tsunamis? 

 Investments: offshore structural characterizations 

and high-resolution elevation data (D, E in table 1’s 

list). 

 Products: hazard and risk assessments, databases, 

event scenarios, and simulations conveying information about offshore faults and potential submarine 

landslides, their potential to generate tsunamis, and 

their effects on coastal natural and built environments (table 1). 

5. How will the built environment respond to strong shaking, particularly from a great (M8–9) subduction zone 

earthquake? 

 Investments: dense onshore seismic monitoring 

and three-dimensional subsurface models (A, F in 

table 1’s list).

 Products: high-resolution hazard and risk assessments and scenarios (table 1), ground-motion simulations and prediction equations. 

Theme 3: Forecasting and Situational 

Awareness

The ability to deliver accurate forecasts and warnings 

needs to be developed before hazardous events occur. Monitoring networks and scientific observations provide critical 

baseline information, which is best obtained by combining different measurement types made continuously in near-real time. 

We suggest that scientists continue to collaborate closely with 

emergency managers and others responsible for disseminating 

information and making actionable decisions. Building on a 

solid foundation of existing capabilities and recent scientific 

and technologic advances, major improvements to existing 

tools are being made and entirely new forecasting ones are 

becoming available. These new tools are described in the 

sections “Gaps in Knowledge and Capabilities and Frontiers 

of Scientific Research” and “Key Investments and Products.” 

Topics are ordered roughly from broadest to most narrow 

in scope. 

A Foundation of Accomplishments and 

Capabilities

Earthquake monitoring is a fundamental component 

of the USGS’s mission. The USGS’s National Earthquake 

Information Center delivers authoritative products (like 

ShakeMaps) about significant earthquakes; these information 

products have grown in sophistication and provide the basis 

for decisions that affect thousands of lives and billions of 

dollars in economic activity. As part of the Advanced National 

Seismic System and in collaboration with universities, the 

USGS operates extensive earthquake monitoring networks in 

California, Oregon, Washington, and Alaska. The USGS and 

its partners also monitor the Nation’s volcanoes, and in both 

cases monitoring data are used for research, hazard assessments, and public/agency awareness and emergency response. 

Also, the USGS-led National Strong Motion Project operates 

instruments throughout the U.S. in high-hazard areas that 

detect strong ground motion, building response, and potential 

structural damage during earthquakes. The most recent monitoring development is the ShakeAlert system for earthquake 

early warning (EEW), which, when completed, will detect an 

earthquake and provide warnings of the impending arrival of 

destructive seismic waves within seconds to minutes. These 

warnings are sufficient to automatically send alerts to people 
Science Themes of the Subduction Zone Science Plan 25

to seek cover, stop trains, open elevator doors, safely close off 

flows through utility and other pipelines, and shut down equipment in operation. Developing an earthquake early warning 

system for Cascadia presents unique challenges and provides 

lessons for instrument deployments in other subduction zones, 

given their unique potential for earthquakes that take hundreds 

of seconds to rupture faults thousands of kilometers long, the 

diversity of earthquake types, and location of major faults 

beneath the ocean. For example, the initial estimate of the 

earthquake’s size is completed just a few seconds after the 

fault begins to slip, while the earthquake is still developing, 

and uses measurements made at onshore instruments far from 

the rupturing fault. These factors introduce serious uncertainties in estimates of magnitude, location, mechanism and, thus, 

expected ground shaking. The earthquake early warning effort 

in the Pacific Northwest will benefit from lessons learned 

during collaborations between the USGS and Japanese colleagues, who are already operating earthquake and tsunami 

early warning systems, and with Chilean colleagues who are 

currently developing these systems.

The USGS is building on its experience forecasting 

aftershocks in California and is expanding this capability to 

all parts of the Nation, including subduction zones. Forecasts 

include the probability of an aftershock that is larger than the 

mainshock. Expansion of routine aftershock forecasting to 

include subduction zone earthquakes requires both the geological understanding of the complexity of earthquake types in 

subduction zones, and a social science understanding of how 

best to deliver forecasts (Wein and others, 2016), particularly 

in communities that are less aware of and prepared for earthquakes than in California. 

The USGS issues timely warnings of a variety of potential volcanic hazards to the public, land managers, emergency 

responders, and to other government agencies, including 

reports on the location and altitude of volcanic ash in the 

atmosphere and potential for volcanic mudflows (lahars). 

In 1982 and 1989, fully loaded passenger jets flying above 

Indonesia and Alaska inadvertently flew into ash clouds from 

erupting volcanoes and lost power in all engines. Although 

their pilots were able to restart some engines and neither jet 

crashed, the planes suffered serious and costly damage. This 

prompted the USGS to develop the capabilities to forecast ash 

cloud locations and ash concentrations, and to provide this 

information to officials responsible for aviation safety. Ash 

cloud warnings are issued for the aviation industry in partnership with the National Weather Service Volcanic Ash Advisory Centers, which enables airplanes to avoid hazardous ash 

clouds and minimizes economic losses caused by cancelled 

flights. At the more local scale, user-friendly maps convey the 

likely paths of lahars during a volcanic eruption. For example, 

the USGS, together with the Washington State and Pierce 

County Emergency Management Departments, operates a 

lahar detection system designed and installed by the USGS in 

the 1990s that can issue warnings to residents in the paths of 

lahars from the northwest drainages of Mount Rainier (fig. 4).

The USGS has developed approaches for forecasting 

rainfall- and earthquake-induced landslides and has applied 

these approaches to produce landslide-hazard maps for average rainfall conditions for some regions. In southern California, USGS estimates of rainfall thresholds above which 

landslides are expected to occur are combined with real-time 

precipitation observations and forecasts to produce landslide watches and warnings issued by the National Weather 

Service for wildfire-burned areas. The USGS also provides 

near-real-time information about rainfall and landslide potential in Seattle, where landslides of various types are a significant natural hazard (fig. 5); for example, in 1997 more than 

100 landslides and accompanying snow caused $100 million 

in damages and killed a family of four. (See http://landslides.

usgs.gov/monitoring/seattle/). For earthquake-induced 

landslides, the USGS has produced scenario-based hazard 

maps for several regions (for example, Anchorage, Alaska; 

see Jibson and Michael, 2009) and is developing the ability 

to forecast such landslides in near-real-time using shaking 

estimates from ShakeMap.

The USGS supports multiple projects that focus on 

analyzing effects of an event, often conveyed as scenarios, 

that consider cascading social, economic, and environmental 

consequences. The National Earthquake Information Center 

and partner seismic networks of the Advanced National Seismic System produce real and hypothetical (scenario) groundmotions, or ShakeMaps, which feed directly into rapid impact 

assessments (PAGER alerts) used by FEMA and other institutions. The Science Application for Risk Reduction Project 

(SAFRR; https://www2.usgs.gov/natural_hazards/safrr/) collaborates with external stakeholders including local, State, and 

Federal partners to examine hypothetical yet plausible seismic, 

tsunami, and storm events whose physical damages may lead 

to social, environmental, and economic consequences (see 

sidebar about the SAFRR workshop on p. 28). The Department 

of the Interior’s Strategic Sciences Group (https://www.doi.

gov/strategicsciences) is designed to support decision making 

during response to actual events. When deployed, the Strategic 

Sciences Group convenes experts from across multiple disciplines to map out the possible cascading consequences of an 

event and identify interventions to support decision making.

Gaps in Knowledge and Capabilities and 

Frontiers of Scientific Research

Developing Tools for Cascading Hazards

Knowledge and capabilities gap.—In the real world, one 

event may trigger another, yet currently most hazard forecasts 

consider only a single geologic event. In subduction zones, 

earthquake shaking can destabilize slopes that ultimately fail 

and become landslides or submarine sediment flows; rapid 

seafloor faults slipping, submarine landslides, or volcanic 

events can all spawn tsunami waves. The ability to build models that include the interaction of multiple, linked phenomena 
26 Reducing Risk Where Tectonic Plates Collide—A Plan to Advance Subduction Zone Science

Seattle

Portland

Olympia

47°N

46°N

45°N

48°N

123°W 121°W 119°W 117°W

Tacoma

MT. RAINIER

Map area

Active volcano

Inactive volcano

EXPLANATION

WASHINGTON

OREGON

Figure 4. Simplified map of ground-based volcanic hazards from an eruption of 

the most threatening volcano in Cascadia: Mount Rainier, Washington. Lahars 

triggered by edifice collapse or magma melting snow and ice pose greater 

risks to communities than from an eruption itself (simplified from Hoblitt and 

others, 1998).

would more accurately predict the outcomes of major subduction zone events. 

Frontier research.—Multidisciplinary monitoring systems and integrative computer models would provide forecasts 

of cascading geologic events and their impacts. An example of 

multidisciplinary monitoring might include the next generation of lahar warning systems, which could monitor multiple 

drainages simultaneously, detect initiating events like landslides farther upstream to gain more warning time, and provide 

estimates of the size of detected events. Such a system would 

employ available high-resolution topography, predictive flow 

models, new instrumentation, and recent improvements in 

seismic algorithms. Systems like this will be built not only 

with consideration of which natural hazards may occur as 

a cascade of events, but also their potential effects on communities and infrastructure. For example, methods permitting 

quick estimates of the probable fatalities and economic losses 

from earthquake shaking in the PAGER product are being 

extended to include possible effects of landslides and liquefaction (Allstadt and others, 2016). This capability to provide loss 

estimates and other new tools could be further developed to 

account more completely for linkages between earthquakes, 

tsunamis, earthquake-generated land-level changes, and 

volcanic eruptions through partnerships with Federal, State, 

and local emergency management agencies, as well as other 

groups that have experience in modeling losses following 

natural disasters.

Forecasting Coastal Land-Level Changes

Knowledge and capabilities gap.—A major earthquake 

may cause subsidence along hundreds of kilometers of 

coastline with consequent inundation equivalent to hundreds 

of years of sea level rise, and the land-level changes may 

occur quickly—in a matter of seconds—or more slowly, 

over a few months (see sidebar about using satellite images 

to detect changes on p. 29). Though physical models exist 

and may be applied to estimate these land-level changes, no 

tools have been developed to forecast these changes or guide 

recovery decisions.
Science Themes of the Subduction Zone Science Plan 27

Destroyed home,

4 fatalities

Destroyed road

along headscarp

Destroyed homes 

atop failed bluff material

Figure 5. Landslides in Seattle, Washington. These photos of 

typical landslides along Seattle’s coastal bluffs illustrate that 

subduction zone hazards don’t only manifest as infrequent, major 

catastrophes to entire communities; they also impact lives, 

property, and infrastructure regularly in smaller, but still locally 

significant, events. Deep-seated slides, like the one shown in 

the left photograph, involve movement of large masses originally 

rooted in bedrock or relatively old sediments (photograph by 

L. Palmer, Federal Emergency Management Agency). In shallow 

slides, like the one shown in the right photograph, soils and 

younger sediments often rapidly flow downhill (photograph 

copyright 1997, T. Tamura, Seattle Times).

Frontier research.—Forecasts of land-level changes are 

possible using available earthquake scenarios constrained 

by quantitative paleo-ecological studies of past events (for 

example, by dating microorganisms that drowned when land 

sank during an earthquake and were preserved in the soil). 

These predictions could then be updated with measurements 

of land-level changes following a major event, using real-time 

global positioning system (GPS) measurements (relatively 

dense networks exist in Cascadia and parts of Alaska) and 

satellite imagery (including interferometric synthetic aperture 

radar, or InSAR). The existing web-based Coastal Storm Modeling System (https://walrus.wr.usgs.gov/coastal_processes/

cosmos/), developed by the USGS to predict storm-induced 

coastal flooding, erosion, and cliff failures, could be leveraged 

by adding capabilities to convey potential subduction-earthquake-induced coastal change.

Assessing the Effects of Subduction Zone Events on 

Ecosystems

Knowledge and capabilities gap.—In subduction zones, 

ecosystems vary in space and time because of gradual environmental changes, and also because of earthquakes, tsunamis, 

volcanic eruptions, and landslides—events that may cause 

habitat fragmentation or shifts in species abundance and 

composition. For example, a landslide can affect habitats by 

changing river channel dynamics, availability of food sources, 

and microclimates. However, quantitative assessments of the 

likely effects of subduction zone events on ecosystems do 

not exist. 

Frontier research.—Assessing the effects of subduction 

zone events on ecosystems requires collaborations between 

scientists supported by the USGS’s Natural Hazards Mission 

Area programs and the Inland Fisheries and Aquatic Gap Programs in the Ecosystems and Core Science Systems Mission 

Areas. For example, an illustrative collaboration is the recent 

collection of high-resolution, multibeam bathymetry data in 

Prince William Sound, Alaska. The Alaska Department of Fish 

and Game, which is interested in characterizing the environment inhabited by fish populations, provided a ship, and the 

USGS, which is interested in identifying submarine faults and 

unstable slopes, contributed surveying equipment. Bathymetry 

data collected filled needs of each agency: to characterize fish 

habitats and to identify submarine faults, respectively.
28 Reducing Risk Where Tectonic Plates Collide—A Plan to Advance Subduction Zone Science

Regional Workshop to Develop the SAFRR Tsunami Scenario

The U.S. Geological Survey Science Application for Risk 

Reduction (SAFRR) project develops and delivers products 

with and for stakeholders to help communities prepare for 

and be more resilient in the wake of natural disasters. The 

SAFRR product most relevant to subduction zone hazards is a hypothetical scenario examining the expected 

impacts to California from a tsunami generated by a 

magnitude 9.1 earthquake located offshore of the Alaska 

Peninsula (Ross and others, 2013). The results of the 

Tsunami Scenario will help risk and emergency managers 

understand the context and consequences of their decisions about how to most effectively improve preparedness 

and response to tsunamis. The Tsunami Scenario exercise 

involved collaboration between the U.S. Geological Survey 

(USGS), the California Geological Survey, the California 

Governor’s Office of Emergency Services (Cal OES), 

the National Oceanic and Atmospheric Administration 

(NOAA), other Federal, State, County, and local agencies, 

private companies, and academic and other institutions. 

The scenario builds on sound science to estimate many 

aspects of the event’s consequences: physical impacts 

(inundation areas, current velocities in key ports and 

harbors, structural damage), economic consequences, 

environmental and ecological impacts, social vulnerability, 

emergency management and evacuation challenges, and 

policy implications. Once completed, the SAFRR Tsunami 

Scenario results and products were publicly introduced 

in September 2013 through a series of workshops that 

brought together emergency managers, maritime authorities, first responders, elected officials and staffers, the 

business sector, State agencies, local media, scientific 

partners, and special districts such as utilities. SAFRR 

continues to assess the effectiveness of the scenario 

process for target stakeholders to improve similar efforts 

going forward.

Photograph of the SAFRR Tsunami Scenario workshop by Stephanie 

Ross, USGS.

Increasing the Reliability of Earthquake and Tsunami 

Warnings

Knowledge and capabilities gap.—Earthquake early 

warning systems and tsunami warnings currently employ 

monitoring data from seismic instruments, some of which can 

saturate when large ground motions exceed their recording 

range, rendering event size difficult or impossible to estimate. 

Tsunami warnings are issued from NOAA’s Tsunami Warning 

Centers and also use data from their Deep-Ocean Assessment 

and Reporting of Tsunamis (DART) systems (which are buoys 

that measure deep-water pressures as a means of detecting 

unusual water-column heights associated with a tsunami 

wave). However, while the DART data do not saturate, they 

require 10 minutes or more to be received and processed, 

which is useful for tsunamis originating outside the affected 

coastline but is too long to provide sufficient warning to 

coastal communities closest to the source.

Frontier research.—A new generation of monitoring 

network operations will integrate real-time GPS measurements—some acoustically linked from floating GPS receivers to monuments on the seafloor—with measurements from 

the existing earthquake monitoring networks, which use only 

seismic data. Observations made on the seafloor just above 

the rupturing fault are particularly important for accurate and 

rapid characterization of the earthquake and its potential for 

generating strong shaking and tsunami waves.

Providing Reliable, High-Fidelity Volcano Warnings

Knowledge and capabilities gap.—Practical warning 

of volcanic unrest relies on detection and interpretation of 

changes in geologic processes that are often only measurable near or on a volcano, yet many volcanoes have few or no 

monitoring instruments. Volcanic eruptions are often heralded 

by clear precursors in the weeks to months prior, such as 

anomalous seismicity, low-level sound waves, elevated surface 

temperatures, volcanic gas emissions, and measurable ground 

deformation. To determine whether changes in volcano activity are due to movement of magma, of hydrothermal fluids, or 

both requires measurements of several of these precursors and 

thus multiple types of instruments. To make this assessment in 

time to warn and respond requires that data are transmitted in 

near-real-time to analysts.
Science Themes of the Subduction Zone Science Plan 29

Satellites Identify Areas of Tsunami Inundation

Satellite images acquired before and after the 

2004 magnitude 9.2 Indian Ocean earthquake 

provide documentation of widespread destruction by tsunami waves. Vegetation, beaches, 

buildings, and roads are seen in pre-earthquake 

images of the Aceh district on the northwestern 

coast of Sumatra (left), but after the earthquake 

(right), virtually all of the plant life and buildings 

were stripped away, and much of the area is 

submerged (brown area) or was destroyed by 

the tsunami, except for a single mosque (white 

dot). Within hours of the initial tsunami waves’ 

landfall, coastal subsidence resulted in significant erosion and shoreline retreat that continued for weeks and months, while elsewhere 

new beaches developed. All these changes 

affected road repair and redevelopment of 

coastal villages.

After

December 2004

Mosque Mosque

Before

December 2004

Satellite image acquired using Space Imaging’s IKONOS satellite 

and processed by the Centre for Remote Imaging, Sensing and 

Processing (CRISP), National University of Singapore (see 

http://www.crisp.nus.edu.sg/tsunami/ for more information about 

the images).

Frontier research.—Monitoring that combines signals 

from multiple instrument types significantly reduces uncertainty in interpreting potential precursors and can provide 

automated alerts to speed the dissemination of warnings. Such 

monitoring would require increased numbers and new types 

of instruments, noting that some U.S. volcanoes have none or 

just a few seismometers, others have several GPS receivers 

as well, and only the most high-threat volcanoes have other 

types of instruments. For example, the data from new realtime volcanic gas emissions and infrasound (acoustic signals 

not audible by humans, but that travel long distances) sensors deployed near volcano summits, when combined with 

data from seismometers, deformation sensors, and InSAR 

imagery, would reduce ambiguities in the interpretation of 

volcanic unrest.

Projecting Ash Cloud Trajectories More Accurately

Knowledge and capabilities gap.—Uncertainties in 

forecasted volcanic ash cloud volumes, compositions, and 

trajectories still result in significant economic loss. While 

significant progress has been made in forecasting ash cloud 

trajectories, the prolonged closure of European airspace in 

2010 following an eruption in Iceland illustrates how uncertainties in ash cloud dispersal estimates may lead to conservatism with resulting unnecessary inconvenience and economic 

losses. Challenges include learning the tolerances of aircraft 

to ash and accurately estimating and measuring ash concentrations in eruption plumes at various elevations and distances 

from the source.

Frontier research.—Predictive capabilities can be 

improved by integrating satellite data into dispersion and 

ash-grain aggregation models, the output of which is validated 

against measurements of ash concentrations in the field (see 

sidebar below about volcanic ash forecasting). Results of all 

these activities will guide collaborative work with the aviation 

industry to test how much and what types of ingested ash may 

damage jet engines; preliminary experiments of this kind are 

underway in Europe and the United States.

Providing Spatially Varying, Regionally Specific 

Aftershock Forecasts

Knowledge and capabilities gap.—Current aftershock 

forecasts are based on statistical analyses of past sequences 

from subduction zones worldwide, but sequences exhibit tremendous variability in behaviors from one geologic setting to 

another. The aftershock forecasts are updated only using rates 

of aftershocks in the ongoing sequence and do not provide any 

information about the likely locations of aftershocks; this lack 

of spatial information is particularly problematic for large subduction earthquakes, where faults may span hundreds of miles.

Frontier research.—Forecasts that employ new real-time 

GPS data, satellite imagery, and knowledge of fault systems, 
30 Reducing Risk Where Tectonic Plates Collide—A Plan to Advance Subduction Zone Science

Volcanic Ash Forecasting

Volcanic ash hazards are far reaching and disruptive, 

affecting more people, infrastructure, and daily activities 

than any other eruptive phenomena. The U.S. Geological 

Survey (USGS) provides forecasts of expected ash dispersal and deposition using an atmospheric transport model 

called Ash3D. When observations warrant an elevated 

alert level for a particular volcano, USGS scientists use 

Ash3D to simulate the outcome for a reasonable eruption scenario. This example Google Earth view of Ash3D 

output from a Mount St. Helens simulation shows cloud 

concentration (pink and purple area labeled 1); affected 

airports (red dots, labeled 2); the model boundary (white 

box, 3); and an animation tool (horizontal bar at top of the 

image, 4). If an eruption occurs, the forecast is updated 

with observations as they become available, and results 

are posted online and provided to the National Weather 

Service for use in its public ashfall advisories. Real-time 

information also goes to the National Oceanic and Atmospheric Administration’s Aviation Weather Center, which 

issues volcanic ash advisories to the Federal Aviation 

Administration so aircraft can be safely diverted around 

the affected area. This information also is shared with 

officials in other countries, including the Kamchatkan Volcanic Eruption Response Team in the Russian Federation 

and the Tokyo Volcanic Ash Advisory Center in Japan.

EXPLANATION

Cloud concentration 

(milligram per 

cubic meter)

300

100

30

10

2

1

0.3

0.1

Veniaminof volcano in eruption, August 18, 2013. Pulses of ash 

and ballistics erupt from the intracadera cinder cone. Two 

streams of lava flow down the east flank into an ice cauldron 

to produce roiling steam clouds. Photograph by Game McGimsey, Alaska Volcano Observatory/U.S. Geological Survey.
National and Global Partnerships 31

and that integrate slip distributions and physical mechanisms 

controlling interactions between earthquake sources, would 

provide spatially varying probabilities of aftershocks in particular time intervals, tailored for specific regions. Acquisition 

and integration of GPS, satellite, and fault-interaction data will 

also improve the temporal accuracy of aftershock forecasts.

Key Investments and Products

The key investments and products outlined below for 

theme 3, “Forecasting and Situational Awareness” will enable 

the USGS, in collaboration with its partners, to deliver shortterm forecasts and warnings with the spatial resolution needed 

by stakeholders to plan for, and respond to, evolving subduction zone events. Advances of existing capabilities would 

reduce false or inaccurate alarms and missed events, and provide more precise notifications. More specifically, new capabilities would include high confidence in offshore earthquake 

and tsunami warnings, warnings of activity at volcanoes that 

are currently unmonitored or poorly monitored, more accurate ash cloud trajectories, and spatially varying and regionally specific aftershock forecasts (see “Warning systems” in 

table 1 on p. 2). Additionally, new tools can provide forecasts 

that are updated as individual and cascading events evolve. 

Examples include updated forecasts of ash falls and lahars 

during volcanic eruptions and of aftershocks following great 

earthquakes; forecasts of changes in coastal land levels, ecosystems, flooding and erosion (see “New types of forecasts” 

in table 1). These would require investments in dense and 

multidisciplinary onshore monitoring; offshore seismic and 

geodetic monitoring; high-resolution multibeam bathymetry 

offshore, adjacent to airborne and space-based topographic 

imagery onshore; and models that link understanding of and 

simulate multiple phenomena (key investments A, B, C, E, I in 

table 1’s list). 

National and Global Partnerships

Current and Future Domestic Institutional 

Partners

The range of partners that the USGS engages in subduction zone science is already very broad, both nationally and 

internationally. For example, within the NSF, the EarthScope 

and GeoPRISMS programs, as well as core programs within 

the Divisions of Earth and Ocean Sciences, have provided 

both facility and research support for efforts to better monitor and understand subduction zones. The EarthScope Plate 

Boundary Observatory includes extensive geodetic monitoring 

of the Cascadia and Alaska Subduction Zones, and the GeoPRISMS effort has enabled important research in the offshore 

areas of subduction zones. USGS has benefitted from, and 

co-supported, both of these ongoing NSF efforts.

Looking forward, an expanded effort in subduction zone 

science could include additional partners in a number of Federal agencies, State and territorial agencies and interest groups, 

and several scientific and engineering consortia. We highlight 

current and potential collaborative activities with key Federal, 

State, and territorial governments, professional organizations, 

and private sector partners in appendix 1.

The USGS’s partnership with the NSF warrants a special 

mention, because of its past and present strength; the leveraging of expertise and resources of both the NSF and the USGS 

has contributed substantially to the success of the NSF’s 

EarthScope and GeoPRISMS programs. Widespread enthusiasm and significant momentum exist within Earth science 

communities to undertake a subduction zone initiative, envisioned as a multidisciplinary program of monitoring systems 

and scientific studies of one or more subduction zones as an 

integrated system, with significant potential support from the 

NSF. In September of 2016, a workshop convened 250 Earth 

scientists from 21 countries to gather input and start to define 

what an initiative focused on fundamental scientific research 

of subduction zone processes might look like, with a goal of 

preparing a proposal to the NSF (see https://www.iris.edu/

hq/workshops/2016/09/szo_16 for workshop overview and 

report). Earthquake, tsunami, landslide, and volcano hazards 

were highlighted in the workshop and report, and scientists 

described many opportunities for collaborating on the complementary activities described in this science plan and within an 

NSF-supported initiative.

U.S. Geological Survey field engineer Lynn Simmons installs 

new equipment at a former temporary seismic monitoring 

station in Marblemount, Washington, that was part of the 

National Science Foundation’s Transportable Array project. 

The upgraded site will be a permanent earthquake monitoring 

station in the Pacific Northwest Seismic Network, which is 

operated as a partnership between the USGS and the University of Washington. Photograph by Maia ten Brink, IRIS.
32 Reducing Risk Where Tectonic Plates Collide—A Plan to Advance Subduction Zone Science

Shared Scientific Infrastructure

Our understanding of subduction zones would benefit 

from shared scientific data centers, laboratories, field instruments, and computational facilities, which would extend 

observations at minimal cost, maximize efficiencies, and 

facilitate the exchange of data and knowledge. Here we 

outline existing and potential shared onshore and offshore 

instrumentation and facilities, which demonstrate that the 

goals laid out in this science plan are technologically and 

logistically feasible.

Onshore Monitoring and Laboratories

The temporal and spatial scales over which subduction zone processes evolve necessitates monitoring networks 

that are operated collaboratively for years to decades. Such 

a sustained activity requires leadership by a Federal agency 

like the USGS with the support of its partners. Examples are 

the Global Seismographic Network, the ANSS (including new 

instrumentation in support of ShakeAlert), and the developing NVEWS. These and other monitoring networks and the 

diverse organizations that operate them are further detailed in 

appendix 1.

Laboratories critical for studying subduction processes 

are used to measure the eruption ages of volcanic rocks by 

radiometric methods, the chemical and isotopic compositions of volcanic products for the study of the origin, storage, 

and ascent of magmas, the failure behaviors of rocks during 

deformation and faulting, the evolution of rock permeability 

and other rock properties over time at elevated temperatures, 

and the conditions of fluid release during subduction. Some 

of the key laboratories capable of making these measurements 

are operated by the USGS and shared with collaborators, and 

in other cases contractor or collaborator laboratories are used 

to make these measurements. 

The Offshore Frontier

Significant fractions of all active U.S. subduction zones 

lie beneath the ocean, so marine research is essential and 

exciting, but also is challenging. Because the oceans are a 

global resource and their exploration is so costly, international 

and national collaborations are already well established. Several existing programs provide research ships, cabled seafloor observatories, and fund research in new technologies to 

observe the oceans; some of these are described in appendix 1. 

Examples of recent offshore community endeavors focused 

on subduction zones include the NSF-sponsored 2011–2015 

Cascadia Initiative, which deployed a temporary array of 

seafloor seismometers and pressure and temperature sensors 

from northern California to southernmost British Columbia. 

The USGS has led and participated in cruises (funded by the 

USGS, NOAA, and international partners) throughout the 

northeast Caribbean to map bathymetry, image and sample the 

subsurface, and record earthquakes that illuminate active faults 

(see sidebar about Caribbean earthquakes on next page); such 

work contributes directly to assessments of tsunami hazards 

along the U.S. East Coast.

Recovery of data from most ocean-bottom instruments 

traditionally requires laborious and expensive shipboard 

cruises, and data are recovered and analyzed long after the 

measured events occurred. Real-time data, however, are 

provided through the NSF’s Ocean Observatories Initiative 

using fiber-optic cables that extend from the Oregon seashore 

to the Juan de Fuca Ridge’s Axial Seamount volcano, as well 

as Ocean Network Canada’s NEPTUNE fiber-optic cable from 

Vancouver Island to the northern Juan de Fuca Ridge. Complementing these efforts, the USGS is partnering with universities and other institutions to explore other methods than 

cables to transmit data from remote seafloor sensors and that 

are significantly less expensive and may be more geographically distributed. For example, the USGS is helping to develop 

wave gliders that perform as self-powered underwater drones 

that enable acquisition of scientific data using acoustic or optical telemetry from seafloor monitoring stations (see sidebar 

about real-time monitoring from the seafloor on p. 34).

Although advances have been made in seafloor seismology, comparable efforts have not yet been made to measure 

slow deformation of the seafloor. GPS signals cannot be 

transmitted to or from the seafloor, so a variety of approaches 

are being explored to measure slow displacements in the 

marine environment. One promising approach combines GPS 

at the sea surface with acoustic ranging to seafloor transponders, serviced by self-propelling wave-gliders and optical data 

transmission. Testing of new seafloor pressure sensors that 

provide continuous measurements of vertical displacements is 

also underway.

Information Technology and Management

Large monitoring networks and remote sensing systems 

produce high volumes of data that must be transferred, stored, 

analyzed, and shared efficiently. Institutions dedicated to the 

archiving and serving of geophysical and image data include 

the USGS’s Earth Resources Observation and Science (EROS) 

Data Center, the NSF-supported IRIS Data Management Center for seismic data, and UNAVCO (originally the University 

NAVSTAR Consortium, now an independent nonprofit organization) for Global Navigation Satellite System (GNSS) and 

other geodetic data. Besides storing and sharing data, these 

institutions develop data standards and transfer protocols used 

worldwide. Similar community information technology exists 

for the archiving and sharing of the chemical compositions 

and ages of igneous rocks (for example, NAVDAT [North 

American Volcanic and Intrusive Rock Database], GEOROC 

[Geochemistry of Rocks of the Oceans and Continents], 

IEDA [Interdisciplinary Earth Data Alliance], and PetDB 

[Petrologic Database]).
National and Global Partnerships 33

Offshore/Onshore Earthquake Hazard Experiment in the Caribbean

The relative motion of the North American and Caribbean 

Plates (white arrows) at is an oblique angle to the plate 

boundary, which is a complex zone of faults (red lines). 

This oblique motion means the plates are both colliding and sliding past one another. The colliding results in 

subduction, but in combination with other types of faulting 

and geologic processes, and in ways that have changed 

over geologic time. Scientists are only beginning to 

unravel how this complex system works, but knowledge of 

which faults are currently active and moving is revealed 

in the characteristics of recent earthquakes. Methods for 

locating earthquakes use triangulation (signals from at 

least three seismic stations), and are far more accurate 

when instruments are close to and surround earthquakes; 

however, more than half of this complex and poorly 

understood region lies offshore. There are no instruments 

deployed on the seafloor in this area on a permanent 

basis, but the USGS and Woods Hole Oceanographic Institution installed six ocean-bottom seismographs (inset photograph and large green triangles on map) from May 2015 

to March 2016. During this experiment, earthquake activity 

near the Puerto Rico Trench (orange circles) was much 

more accurately characterized; hundreds of earthquakes 

were detected, helping to understand fault motions at 

this subduction zone. The data collected from the temporary offshore seismographs complement those from 

the onshore permanent seismic network stations (small 

inverted green triangles). The last significant plateinterface earthquake in this region was the magnitude 7.1 

Mona Passage event in 1918 (black star on map, which 

generated a tsunami that inundated the northwestern 

coast of Puerto Rico as far as 100 meters (328 feet) inland 

and resulted in 116 fatalities.

PUERTO RICO

HAITI

DOMINICAN

REPUBLIC

M7.8 (1918)

North American Plate

Caribbean Plate

Relative plate motion

20°N

18°N

72°W 68°W 64°W 60°W

Ocean bottom seismograph Map from Andrews and others (2014); 

modified by Nathan Miller, U.S. Geological Survey.

Earthquake epicenters

EXPLANATION

2.5 6.0

Magnitude (M )

0 100

0 100 200 KILOMETERS

200 MILES

This stray coral boulder, which 

was transported by a tsunami from 

offshore to 230 meters inland on 

Anegada, British Virgin Islands, and 

other debris from past tsunamis are 

used to assess earthquake and tsunami hazards of the subduction zone 

and the adjoining outer rise along the 

Puerto Rico trench. U.S. Geological 

Survey photograph by Brian Atwater.
34 Reducing Risk Where Tectonic Plates Collide—A Plan to Advance Subduction Zone Science

Seafloor Real-Time Monitoring

Motivated by the disastrous magnitude 9.0 Tōhoku, Japan, 

earthquake and tsunami and the ensuing loss of life and 

damage to its national economy, Japanese scientists have 

recently installed a new seafloor network of 150 earthquake and tsunami detectors (circles on map, colors 

denote different cable segments) that transmit data to 

land in real time using fiber-optic cables. This network, 

called the Seafloor Observation Network for Earthquakes 

and Tsunamis along the Japan Trench (called S-net for 

short) should provide an extra 20–30 seconds of warning 

of an earthquake and an extra 10 minutes of warning of a 

tsunami. 

In Cascadia, the offshore instrument network that transmits data using seafloor cables is too sparse and slow to 

contribute to early warning systems, and no appropriately 

instrumented cables exist in the other U.S. subduction 

zones. However, a variety of new technologies under 

development, shown in images B, C, and D, below, offer 

alternatives for real-time seafloor monitoring that are far 

less costly and more versatile than cabled systems. For 

example, wave gliders (B ) are self-powered underwater 

drones that can collect data in the ocean and send them 

from the surface for analysis via satellites or radio. They 

operate without environmental impact, cost hundreds of 

times less to operate than traditionally deployed ships, 

and for some applications provide higher-fidelity data. 

For transmitting data from seafloor instruments to wave 

gliders or ships, new optical modems (C ) can transmit at 

high sample rates (for example, for seismic signals) over 

distances of hundreds of feet, acoustic modems (D ) can 

work over thousands of feet but at lower rates, and both 

eliminate the need for expensive and difficult-to-access 

physical connections.

Waveglider photo from Chadwell and others, 2016

Modem photos from Farr and others, 2010

Trench

40°N

42°N

38°N

36°N

34°N

140°E 142°E 144°E 146°E

Map modified from Detweiler, S., and Ellsworth, W., eds., 2015

0 100 KILOMETERS

0 100 MILES

A, Ocean bottom cabled observation network composed of 

seismometers and tsunami meters. B, Wave glider for data 

acquisition and transmission. C, Optical data transmission 

modem. D, Acoustic data transmission modem.

A B

C D
New Community Resources and Engagement 35

Analyses of massive datasets and state-of-the-art modeling also requires high-performance computing capabilities. The USGS’s Advanced Research Computing Program 

facilitates the fulfillment of these needs. USGS researchers 

have benefitted from supercomputing facilities at the NASA 

Ames Research Center, Department of Energy’s (DOE) Pacific 

Northwest and Oak Ridge National Laboratories, and the joint 

USGS-NSF supported Southern California Earthquake Center.

International Activities

Globally, major subduction earthquakes, tsunamis, large 

landslides, and major eruptions take place at intervals of several years. Major events and ongoing research activities related 

to subduction zone geologic processes abroad often affect 

U.S. domestic affairs and can be invaluable learning opportunities. On an ongoing basis, the USGS is a major player in 

global hazard monitoring, disaster assessment, response, and 

in assisting other countries to build internal capabilities for 

these activities; examples include Volcano Disaster Assistance 

Project (VDAP) (see sidebar on next page about VDAP and 

USAID efforts) and Earthquake Disaster Response Teams 

(EDAT) staffed by USGS scientists with support from the 

U.S. Agency of International Development’s Office of Foreign 

Disaster Assistance (OFDA) program. Many of these international activities, and the partnering international programs, 

are described in appendix 2. Ongoing USGS research collaborations with scientists in countries facing subduction zone 

hazards are facilitated by formal agreements with Japan, New 

Zealand, Russia, Canada, China, Italy, and Chile.

New Community Resources and 

Engagement

The USGS seeks to deliver products in ways that meet 

stakeholder needs and to ensure the most current science 

is available to inform decision making in subduction zone 

regions. This section summarizes an envisioned package of 

linked, innovative products and activities meant to address 

stakeholder needs, many of which also have application to a 

broader array of societal needs.

Products

• Systematically acquired high-resolution bathymetry 

and topographic mapping data and subsurface imagery

will be community resources. A precedent exists in 

the Pacific Northwest, where consortia for the Puget 

Sound region and the States of Oregon and Idaho bring 

together State, Tribal, Federal, private, and academic 

institutions to coordinate acquisition and distribution of 

light detection and ranging imagery (called lidar, which 

is remotely sensed, digital topographic data) to be 

used for urban and county planning, forest and habitat 

management, and geological studies. The exceptional 

spatial resolution provided by airborne lidar imagery 

has dramatically improved the USGS’s ability to map 

a broad suite of natural hazards, including recent and 

prehistoric fault scarps left by earthquakes, lava flows, 

magma domes, debris flows, lahars, and landslides. 

The combination of lidar and multibeam echo-sounder 

bathymetry data would allow detailed, seamless mapping of both the land and the seafloor, which would 

have wide-ranging applications for hazards studies, 

fish and wildlife management, siting and safety of 

seafloor cables and infrastructure, national defense, and 

coastal erosion studies.

• The USGS’s 3DEP (three-dimensional elevation 

program), programs in the Natural Hazards Mission 

Area and others have partnered with many agencies to 

acquire lidar and bathymetric data, including NASA, 

NOAA, Bureau of Ocean Energy Management, U.S. 

Department of Agriculture (USDA) Forest Service, 

U.S. Army Corps of Engineers, Bureau of Reclamation, the Alaska Department of Fish and Game, Oregon 

Department of Geology and Mineral Industries, Washington State Department of Natural Resources, and 

numerous other State, county, and city governments. 

The USGS also partners with international governments (such as the Canadian Geological Survey), 

public utility districts, private industry, and academic 

groups, further demonstrating the universal value of 

high-resolution topographic and bathymetric data (see 

sidebar about how to identify local tsunami hazards on 

p. 23).

• A comprehensive, public database of active faults near 

areas with dense population and critical infrastructure, 

both on land and offshore, builds on USGS expertise 

and existing products. For example, recent mapping 

suggests numerous faults in these densely populated 

areas may be active, but for many known faults there 

is insufficient information to determine past rates of 

movement and likely future ruptures. Studies to gather 

this information are needed—the USGS Quaternary 

Fault and Fold Database (http://earthquake.usgs.gov/

hazards/qfaults/) is very incomplete. Great subduction 

zone earthquakes occur along the interface between 

colliding plates, but experience and research show that 

local earthquakes on shallow crustal faults may be 

more hazardous if located near urban areas and critical 

infrastructure.

• Accurate community-accepted models of geologic 

structures, regional-scale fault systems, and tectonic 
36 Reducing Risk Where Tectonic Plates Collide—A Plan to Advance Subduction Zone Science

Partnering with USAID for Science and Humanity

The Volcano Disaster Assistance Program (VDAP) is the 

international arm of the U.S. Geological Survey (USGS) 

Volcano Hazards Program, which is partly funded by 

the U.S. Agency for International Development’s Office 

of Foreign Disaster Assistance (USAID/OFDA). For the 

past 30 years, VDAP has strived to reduce loss of life and 

property by enhancing volcano monitoring and eruption 

response capabilities of nations around the world. In addition to building in-country capacity for host nations, VDAP 

maintains a team of experienced volcano-disaster scientists ready to respond to volcanic unrest with the latest 

tools and methods. In this photograph (by Chistoph Kern, 

USGS), USGS and Indonesian scientists install monitoring 

equipment at Sinabung volcano in 2016. USAID/OFDA also 

partners with USGS on an Earthquake Disaster Assistance 

Team (EDAT) of USGS scientists who work with local and 

national governments in countries affected by damaging 

earthquakes to improve understanding of seismic hazards 

and develop appropriate building codes and land-use 

plans. To date, EDAT has collaborated with scientists in 

China, Comoros, Haiti, Indonesia, Malawi, Nepal, and 

Turkey. Following the 2015 magnitude 7.8 earthquake in 

Nepal, for example, a six-person EDAT-supported team 

installed low-cost seismic monitoring instruments, conducted instrument training sessions, assisted with data 

analysis, documented earthquake-induced landslides and 

liquefaction, and helped assess ongoing landslide hazard 

in preparation for the 2015 monsoon season.

Monitoring equipment being installed at Sinabung volcano in Indonesia on August 14, 2016. Photograph from Christoph Kern, USGS.

Damaged shoreline 

at Lhoknga, Indonesia, following 

the December 

2004 Indian Ocean 

tsunami. U.S. Geological Survey 

photograph by Guy 

Gelfenbaum.
New Community Resources and Engagement 37

motions have proven to be valuable resources for 

research, engineering, and outreach products in southern California (https://www.scec.org/research/usr); 

development of similar such community models for the 

Nation’s subduction zones will provide shared frameworks that enable integration of results from a diversity 

of studies, and serve as common foundations for more 

detailed explorations.

• A seamless onshore/offshore subduction zone series of 

digital maps (of topography, faults, geologic structures, 

rock and sediment types, and so on) and an interactive 

mapping application will serve as a platform for 

integration of research, resource management, hazards 

mitigation and response, and public education. The 

USGS-led California Seafloor and Coastal Mapping 

Program (https://walrus.wr.usgs.gov/mapping/csmp/) 

provides an example of an innovative framework 

for scientific research, coastal planning, and public 

engagement through the online release of all project 

data, including a user-friendly video and photograph 

portal and interactive web services for visualizing and 

analyzing large geospatial datasets. The application 

could be linked to an enhanced fault database with 

fault information that is digital, understandable and 

useful to both technical and non-technical users, and 

easily integrated into other applications, such as insurance risk models, and new development planning by 

city engineers and private developers. (The existing 

USGS Quaternary Fault and Fold Database contains 

only textual, technical descriptions.)

• Web-enabled three-dimensional visualizations have 

the potential to convey the complexities of subduction 

zone processes so they are understandable and interesting, both for the general public and scientific researchers. Together with partners from NASA, the USGS 

can leverage their experience making the mysteries 

of outer space accessible and exciting to the public 

through use of computer visualization tools (such as 

NASA’s World Wind interface, at https://worldwind.

arc.nasa.gov/) that could be adapted to do the same 

for subduction zones. These interactive tools also help 

scientists to visualize the information contained in 

large datasets, to integrate multiple datasets, and to 

understand them in the context of complex, intertwined 

physical processes. For example, new insights about 

how faulting and earthquakes evolve over millennia 

have resulted from the ability to visualize the predictive models of how faults relieve stresses in complex, 

three-dimensional fault networks. Visualization tools 

also allow model-predicted parameters to be compared 

with real measurements.

• Experience with the scenarios noted throughout this 

plan indicates the potential for regionally focused, 

publicly available libraries of risk-based scenarios for 

the full range of subduction zone events, and perhaps 

even cascades of events, that would be widely used 

in engineering design, emergency management plans 

and exercises, insurance projections, and infrastructure 

planning. 

Outreach and Education

Workshops with user groups, webinars and online 

courses, surveys, and participation in professional society activities engage users and evaluate the efficacy of our 

products. Activities and products described in this Subduction 

Zone Science Plan will follow guidelines on how to effectively 

communicate scientific information to others developed by a 

diverse group of risk communication experts from the USGS 

and universities (Perry and others, 2016). Experts in hazard 

and risk communications with stakeholders from the USGS’s 

SAFRR project also would be engaged to ensure the application of scientific discoveries and products fills stakeholders’ 

needs (see sidebar story on p. 26). 

The inevitability of great earthquakes, tsunamis, volcanic 

eruptions, coupled with the potential for scientific discovery 

and the development of new exploration tools, particularly in 

the offshore reaches of subduction zones, provide tremendous 

opportunity to capture the public’s imagination and educate 

communities about the hazards they face. For example, engaging and educational imagery may be conveyed to the public 

via webcam and (or) through easy-to-use online geospatial 

viewers like the USGS Video and Photograph Portal for 

the Coastal and Marine Geology program (http://cmgvideo.

usgsportals.net/). Additionally, the USGS’s established presence on various social media platforms such as Facebook, 

Google Plus, Twitter, and others may be expanded to educate 

the public about subduction zone science discoveries, and to 

both gather and distribute hazard information.

Ensuring continued development of effective products 

requires the training of students in the science of hazard and 

risk assessment. Training includes topics from the social 

sciences, such as user-centered design and risk messaging. 

Example topics from the physical sciences include statistical methods for incorporating field observations of ash flow 

deposits into probabilities of future eruptions, and application 

of computer simulations of earthquakes on complex fault networks. The varied and significant potential hazards associated 

with subduction zone processes make related research and 

activities ideal opportunities for hands-on learning, through 

USGS internships, post-doctoral and volunteer programs, and 

through teaching at partner universities. 

Finally, the USGS will continue its strong tradition of 

educating the public through individual scientist participation 

in and institutional support of professional societies and consortia, particularly those concerned directly or indirectly with 

subduction zone geologic processes.
38 Reducing Risk Where Tectonic Plates Collide—A Plan to Advance Subduction Zone Science

Geologists drive a core into marsh 

sediment to document interbedded 

peat and silt that records sudden vertical land movements associated with 

fault slip during large subduction-zone 

earthquakes. U.S. Geological Survey 

photograph by Rich Briggs.

Data Management Plan

To achieve the USGS mission of providing scientific data 

that serves the Nation, the data and science products described 

herein will be peer reviewed, made widely available, and managed for long-term storage. Under the authority of the USGS 

Community for Data Integration, all data and products from 

the Subduction Zone Science Plan will be made available to 

the public for posterity through a suite of web applications, 

spatial data tools, and archival resources.

Acknowledgments

This report was supported by the U.S. Geological Survey 

Natural Hazards Mission Area. The Subduction Zone Science 

Plan reflects the ideas of Annemarie Baltay, Nicholas Beeler, 

Scott Bennett, Michael Blanpied, Amy East, Eileen Evans, 

Carol Finn, Jonathan Hagstrum, Anna Kelbert, Jared Kluesner, 

Nicolas Luco, John Lyons, Nathaniel Miller, Alan Nelson, 

Jared Peacock, Jonathan Perkins, Mark Petersen, Geoffrey 

Phelps, Cyrus Read, Bruce Richmond, Daniel Scheirer, 

Kevin Schmidt, David Scholl, Lydia Staisch, Weston Thelan, 

Roland von Huene, Aaron Wech, Robert Witter, and William 

Yeck. The writing team thanks Kate Allstadt, David Applegate, Brian Atwater, Susan Benjamin, Jonathan Godt, Gavin 

Hayes, Stephen Hickman, Jill McCarthy, Seth Moran, Alice 

Pennaz, John Power, Jane Reid, Stephanie Ross, Uri ten 

Brink, Greg Shelton, Colin Williams, and Nate Wood for their 

valuable reviews.

References Cited

Allstadt, K.E., Thompson, E.M., Wald, D.J., Hamburger, 

M.W., Godt, J.W., Knudsen, K.L., Jibson, R.W., Jessee, 

M.A., Zhu, Jing, Hearne, Michael, Baise, L.G., Tanyas, 

Hakan, and Marano, K.D., 2016, USGS approach to realtime estimation of earthquake-triggered ground failure—

Results of 2015 workshop: U.S. Geological Survey OpenFile Report 2016–1044, 13 p., http://dx.doi.org/10.3133/

ofr20161044.

Andrews, B.D., ten Brink, U.S., Danforth, W.W., Chaytor, 

J.D., Granja Bruña, José-Luis, Llanes Estrada, Pilar, and 

Carbó-Gorosabel, Andrés, 2014, Bathymetric terrain model 

of the Puerto Rico trench and the northeastern Caribbean 

region for marine geological investigations: U.S. Geological 

Survey Open-File Report 2013–1125, 10 p., 1 pl., 

http://dx.doi.org/10.3133/ofr20131125.

Atwater, B.F., Musumi-Rokkaku, S., Satake, K., Tsuji, Y., 

Ueda, K., and Yamaguchi, D.K., 2015, The orphan tsunami 

of 1700—Japanese clues to a parent earthquake in North 

America (2d ed.): Seattle, University of Washington Press, 

U.S. Geological Survey Professional Paper 1707, 135 p. 

[Also available online at http://dx.doi.org/10.3133/pp1707.) 

Beget, J.E., 2000, Volcanic Tsunamis in Sigurdsson H., ed., 

Encyclopedia of Volcanoes: San Diego, Calif., Academic 

Press, p. 1005–1013.
References Cited 39

Brothers, D.S., Haeussler, P.J., Liberty, L., Finlayson, D., 

Geist, E., Labay, K., and Byerly, M., 2016, A submarine landslide source for the devastating 1964 Chenega 

tsunami, southern Alaska: Earth and Planetary Science 

Letters, v. 438, p. 112–121, http://dx.doi.org/10.1016/j.

epsl.2016.01.008.

Chadwell, C.D., Webb, S., and Nooner, S., 2016, Campaignstyle GPS-Acoustic with wave gliders and permanent seafloor benchmarks: accessed May 17, 2017, at https://www.

iris.edu/hq/files/workshops/2016/09/szo_16/whitepapers/

chadwell_gpsa_wp.pdf.

Coats, R.R., 1962, Magma type and crustal structure in the 

Aleutian arc in Macdonald, G.A., and Kuno, H., eds., 

The crust of the Pacific basin: Geophysical Monograph 6, 

p. 92–109.

Detweiler, S., and Ellsworth, W., eds., 2015, Proceedings 

of the 9th U.S.-Japan natural resources panel for earthquake research: U.S. Geological Survey Open-File Report 

2014–1250, 89 p., accessed May 17, 2017, at https://dx.doi.

org/10.3133/ofr20141250. 

Ewert, J.W., Guffanti, M., and Murray, T.L., 2005, An assessment of volcanic threat and monitoring capabilities in the 

United States—Framework for a national volcano early 

warning system: U.S. Geological Survey Open File Report 

2005–1164, 62 p. [Also available online at https://pubs.usgs.

gov/of/2005/1164/2005-1164.pdf.]

Farr, N., Bowen, A., Ware, J., Pontbriand, C., and Tivey, M., 

2010, An integrated, underwater optical/acoustic communications system: accessed May 17, 2017, at https://www.

whoi.edu/fileserver.do?id=64583&pt=2&p=76726.

Frankel, A.D., Stephenson, W.J., Carver, D.L., Williams, R.A., 

Odum, J.K., and Rhea, S., 2007, Seismic hazard maps for 

Seattle, Washington, incorporating 3D sedimentary basin 

effects, nonlinear site response, and rupture directivity, 

U.S. Geological Survey Open-File Report 2007–1175, 

77 p., 3 plates. [Also available online at https://pubs.usgs.

gov/of/2007/1175/.]

Godt, J.W., Baum, R.L., Savage, W.Z., Salciarini, D., Schulz, 

W.H., and Harp, E.L., 2008, Transient deterministic shallow 

landslide modeling—Requirements for susceptibility and 

hazard assessments in a GIS framework: Engineering Geology, v. 102, p. 215–227, doi:10.1016/j.enggeo.2008.03.019.

Goldfinger, C., Galer, S., Beeson, J., Hamilton, T., Black, B., 

Romsos, C., Patton, J., Nelson, C.H., Hausmann, R., and 

Morey, A., in press, The importance of site selection, sediment supply, and hydrodynamics—A case study of submarine paleoseismology on the northern Cascadia margin, 

Washington, USA: Marine Geology, 36 p., http://dx.doi.

org/10.1016/j.margeo.2016.06.008

Guffanti, M., and Muffler, L.J.P., 1995, Geothermal potential 

of diverse volcanotectonic settings of the Cascade Range, 

USA: International Geothermal Assembly, v. 2, Proceedings 

of the World Geothermal Congress, p. 719–724.

Heaton, T.H., and Hartzell, S.H., 1987, Earthquake hazards on 

the Cascadia subduction zone: Science, v. 236, p. 162–168.

Hoblitt, R.P., Walder, J.S., Driedger, C.L., Scott, K.M., Pringle, P.T., and Vallance, J.W., 1998, Volcano hazards from 

Mount Rainier, Washington, revised 1998: U.S. Geological 

Survey Open-File Report 98–428, 11 p. [Also available 

online at https://pubs.usgs.gov/of/1998/0428/.]

Holmes, R.R., Jr., Jones, L.M., Eidenshink, J.C., Godt, J.W., 

Kirby, S.H., Love, J.J., Neal, C.A., Plant, N.G., Plunkett, 

M.L., Weaver, C.S., Wein, Anne, and Perry, S.C., 2013, 

U.S. Geological Survey natural hazards science strategy—

Promoting the safety, security, and economic well-being 

of the Nation: U.S. Geological Survey Circular 1383–F, 

79 p., accessed November 2016 at https://pubs.usgs.gov/

circ/1383f/. 

Hyndman, R.D., 1995, Giant earthquakes of the Pacific Northwest: Scientific American, v. 273, p. 50–57.

Iinuma, T., Hino, R., Kido, M., Inazu, Osada, Y., Ito, Y., 

Ohzono, M., Tsushima, H., Suzuki, S., Fujimoto, H., 

and Miura, S., 2012, Coseismic slip distribution of 

the 2011 off the Pacific Coast of Tohoku Earthquake 

(M9.0) refined by means of seafloor geodetic data: Journal of Geophysical Research, v. 117, B07409, 18 p., 

doi:10.1029/2012JB009186.

Ito, Y., Hino, R., Kido, M., Fujimoto, H., Osada, Y., Inazu, 

D., Ohta, Y., Iinuma, T., Ohzono, M., Miura, S., Mishina, 

M., Suzuki, K., Tsuji, T., and Ashi, J., 2013, Episodic slow 

slip events in the Japan subduction zone before the 2011 

Tohoku-Oki earthquake: Tectonophysics, v. 600, p. 14–26.

Jibson, R.W., and Michael, J.A., 2009, Maps showing seismic 

landslide hazards in Anchorage, Alaska: U.S. Geological 

Survey Scientific Investigations Map 3077, 11 p., scale 

1:25,000. [Also available online at https://pubs.usgs.gov/

sim/3077.]

Kodaira, S., No, T., Nakamura, Y., Fujiwara, T., Kaiho, 

Y., Miura, S., Takahashi, N., Kaneda, Y., and Taira, A., 

2012, Coseismic fault rupture at the trench axis during 

the 2011 Tohoku-oki earthquake: Nature Geoscience, v. 5, 

p. 646–650, doi:10.1038/ngeo1547. 

Lipman, P.W., and Mullineaux, D.R., 1981, The 1980 eruptions of Mount St. Helens, Washington: U.S. Geological 

Survey Professional Paper 1250, 844 p. [Also available 

online at https://pubs.er.usgs.gov/publication/pp1250.]
40 Reducing Risk Where Tectonic Plates Collide—A Plan to Advance Subduction Zone Science

Menzie, W.D., Baker, M.S., Bleiwas, D.I., and Kuo, Chin, 

2011, Mines and mineral processing facilities in the vicinity of the March 11, 2011, earthquake in northern Honshu, 

Japan: U.S. Geological Survey Open-File Report 2011–

1069, 7 p. 

Muffler, L.J.P., and Tamanyu, S., 1995, Tectonic, volcanic, and 

geothermal comparison of the Tohoku volcanic arc (Japan) 

and the Cascade volcanic arc (USA): International Geothermal Assembly, v. 2, Proceedings of the World Geothermal 

Congress, p. 725–730.

Perry, S.C., Blanpied, M.L., Burkett, E.R., Campbell, N.M., 

Carlson, A., Cox, D.A., Driedger, C.L., Eisenman, D.P., 

Fox-Glassman, K.T., Hoffman, S., Hoffman, S.M., Jaiswal, 

K.S., Jones, L.M., Luco, N., Marx, S.M., McGowan, 

S.M., Mileti, D.S., Moschetti, M.P., Ozman, D., Pastor, E., 

Petersen, M.D., Porter, K.A., Ramsey, D.W., Ritchie, L.A., 

Fitzpatrick, J.K., Rukstales, K.S., Sellnow, T.S., Vaughon, 

W.L., Wald, D.J., Wald, L.A., Wein, A., and Zarcadoolas, 

C., 2016, Get your science used—Six guidelines to improve 

your products: U.S. Geological Survey Circular 1419, 37 p., 

http://dx.doi.org/10.3133/cir1419.

Phipps, J.B., Hemphill-Haley, E., and Atwater, B.F., 2015, 

Chance findings about early Holocene tidal marshes of 

Grays Harbor, Washington, in relation to rapidly rising seas 

and great subduction earthquakes (ver. 1.1, May 2016): 

U.S. Geological Survey Scientific Investigations Report 

2015–5063, 36 p., http://dx.doi.org/10.3133/sir20155063.

Plafker, G., 1965, Tectonic deformation associated with the 

1964 Alaska earthquake: Science, v. 148, p. 1675–1687.

Ross, S.L., Jones, L.M., Miller, K., Porter, K.A., Wein, A., 

Wilson, R.I., Bahng, B., Barberopoulou, A., Borrero, J.C., 

Brosnan, D.M., Bwarie, J.T., Geist, E.L., Johnson, L.A., 

Kirby, S.H., Knight, W.R., Long, K., Lynett, P., Mortensen, 

C.E., Nicolsky, D.J., Perry, S.C., Plumlee, G.S., Real, C.R., 

Ryan, K., Suleimani, E., Thio, H.K., Titov, V.V., Whitmore, 

PM., and Wood, N.J., 2013, SAFRR (Science Application 

for Risk Reduction) Tsunami Scenario—Executive summary and introduction: U.S. Geological Survey Open-File 

Report 2013–1170–A in Ross, S.L., and Jones, L.M., eds., 

The SAFRR (Science Application for Risk Reduction) Tsunami Scenario: U.S. Geological Survey Open-File Report 

2013–1170, 17 p., accessed November 2016, at http://pubs.

usgs.gov/of/2013/1170/a/.

Sato, M., Fujita, M., Matsumoto, Y., Ishikawa, T., Saito, H., 

Mochizuki, M., and Asada, A., 2013, Interplate coupling off 

northeastern Japan before the 2011 Tohoku-oki earthquake, 

inferred from seafloor geodetic data: Journal of Geophysical 

Research, v. 118, p. 3860–3869, doi:10.1002/jgrb.50275.

Schulz, K., 2015, The really big one: The New Yorker, 

July 20, 2015 issue, 13 p.

Simkin, T., Tilling, R.I., Vogt, P.R., Kirby, S.H., Kimberly, P., 

and Stewart, D.B., 2006, This Dynamic Planet—World Map 

of Volcanoes, Earthquakes, Impact Craters, and Plate Tectonics (3d ed.): U.S. Geological Survey Geologic Investigations Map I-2800, accessed February 2017, at https://pubs.

usgs.gov/imap/2800/.

Suleimani, E.N., Haeussler, P.J., and Hansen, R.A., 2009, 

Numerical study of tsunami generated by multiple submarine slope failures in Resurrection Bay, Alaska, during the 

Mw9.2 1964 earthquake: Pure and Applied Geophysics, 

v. 166, p. 131–152.

Tappin, D.R., Grilli, S.T., Harris, J.C., Geller, R.J., Masterlark, 

T., Kirby, J.T., Fengyan, S., Ma, G., Thingaijam, K.K.S., 

and Mai, P.M., 2014, Did a submarine landslide contribute 

to the 2011 Tohoku tsunami?: Marine Geology, v. 357, 

p. 344–361.

ten Brink, U.S., Chaytor, J.D., Geist, E.L., Brothers, D.S., and 

Andrews, B.D., 2014, Assessment of tsunami hazard to the 

U.S. Atlantic margin: Marine Geology, v. 353, p. 31–54.

Tsunami Pilot Study Working Group, 2006, Seaside, Oregon, 

tsunami pilot study–Modernization of FEMA flood hazard 

maps: U.S. Geological Survey Open-File Report 2006–

1234, 57 p., accessed December 2016, at https://pubs.usgs.

gov/of/2006/1234/of2006-1234.pdf.

Wech, A.G., 2016, Extending Alaska’s plate boundary—Tectonic tremor generated by Yakutat subduction: Geology, 

v. 44, p. 587–590, doi:10.1130/G37817.1.

Wein, A., Potter, S., Johal, S., Doyle, E., and Becker, J., 2016, 

Communicating with the public during and earthquake 

sequence—Improving communication of geoscience by 

coordinating roles: Seismological Research Letters, v. 87, 

p. 112–118, doi:10.1785/0220150113.

Wood, N., Jones, J., Schmidtlein, M., Schelling, J., and 

Frazier, T., 2016, Pedestrian flow-path modeling to support tsunami evacuation and disaster relief planning 

in the U.S. Pacific Northwest: International Journal of 

Disaster Risk Reduction, v. 18, p. 41–55, doi:10.1016/j.

ijdrr.2016.05.010.
Appendixes

A U.S. Geological Survey scientist installs an air-quality monitor in Unalaska, Alaska, during the 

eruption of Bogoslof Volcano in February 2017. Alaska Volcano Observatory/U.S. Geological 

Survey photograph by Janet Schaefer.
42 Reducing Risk Where Tectonic Plates Collide—A Plan to Advance Subduction Zone Science

Appendix 1. Selected Current and Potential Partnerships

The USGS has a strong tradition of leveraging its assets 

by partnering with a wide range of public and private-sector 

institutions. Advancing subduction zone science in the significant ways described in this plan will require nurturing existing 

partnerships and developing new ones. This appendix summarizes many of these collaborations in order to demonstrate 

that, indeed, this type of cooperative science can be done and 

can give rise to new discoveries, technologies, and capabilities 

that save lives and property.

U.S. Governmental, Professional, and Private 

Entities

Federal Agencies

• The National Science Foundation’s (NSF) Division of 

Earth Sciences (EAR) currently supports the EarthScope facility and research program; the Plate Boundary Observatory and Transportable Array, operated 

by the EarthScope program, have direct applicability 

to subduction zone science. EAR also supports the 

Global Seismographic Network and the Continuously 

Operating Caribbean GPS Observational Network 

(COCOnet). The Division of Ocean Sciences (OCE) 

supports the International Ocean Discovery Program 

(IODP) and the Ocean Observatory Initiative (OOI). 

The cross-division initiatives at NSF that are directly 

related to subduction zone science include GeoPRISMS, the Cascadia Initiative, and the Trans-boundary, Land and Atmosphere Long-Term Observational 

and Collaborative Network (TLALOC) in Mexico. 

Other relevant NSF initiatives include the Prediction of 

and Resilience against Extreme Events (PREEVENTS) 

research initiative. NSF also supports high-performance computing that could be integrated into various 

subduction zone modeling efforts. In October 2016, 

the NSF sponsored a scientific community workshop 

in support of possible development of a proposal for 

a new initiative focused on subduction zones. USGS 

would closely coordinate its plans and activities with 

such a proposal and program, so that they maximally 

complement one another.

• The National Oceanographic and Atmospheric Administration (NOAA) already partners with the USGS for 

tsunami monitoring, warning and hazard assessment. 

Activities related to bathymetric mapping and tsunami 

source modeling are coordinated through the National 

Tsunami Hazard Mitigation Program, which includes 

participants from all U.S. tsunami-vulnerable States, 

territories, and regions. The USGS’s National Earthquake Information Center (NEIC) routinely provides 

seismic data and derived information to the NOAA’s 

Tsunami Warning Centers. This collaboration could be 

extended through new USGS investments in geodetic 

networks, lidar imagery collection, and other mapping 

efforts. NOAA is also responsible for atmospheric 

monitoring, including the presence of volcanic ash 

clouds, and issues volcanic ash advisories through its 

Volcanic Ash Advisory Centers (VAAC) in Anchorage, Alaska; Washington, D.C.; and seven other cities 

outside the United States. The basis for these warnings 

comes from information provided by USGS Volcano 

Observatories.

• The National Aeronautics and Space Administration 

(NASA) currently partners with the USGS, NOAA, 

and NSF to compile hazard-related data, conduct 

research, and deliver post-disaster products. NASA cosupports UNAVCO, a nonprofit organization that helps 

scientists collect geodetic data, which operates data 

acquisition form the Global Navigation Satellite System (GNSS). NASA is currently working with NOAA 

to integrate real-time, GNSS-derived displacements to 

the NOAA Tsunami Warning Centers. NASA is also 

planning to launch a radar satellite (operated jointly by 

the United States and India, called NISAR), which will 

provide a wealth of imagery data that will transform 

research on the Earth’s surface —in subduction zones 

and elsewhere. NASA’s Disasters Applications project 

supports research and other activities to improve the 

prediction, preparation, response and recovery to 

natural disasters. Combining the unique capabilities 

of NASA to acquire and analyze data from space with 

the USGS’s terrestrial monitoring and geologic studies 

would strengthen the research and products of both 

agencies. 

• The Office of Foreign Disaster Assistance (OFDA) 

of the U.S. Agency for International Development 

currently supports the USGS to engage internationally 

in volcanic eruption response and scientific capacity building (through the Volcano Disaster Assistance 

Project, or VDAP), and earthquake disaster response 

(through the Earthquake Disaster Assistance Team, or 

EDAT), both of which are described in the “International Activities” section of this plan and in the sidebar 

“Partnering with USAID for Science and Humanity.” OFDA also supports USGS development of an 

earthquake and tsunami early warning system in Chile 

and an operational aftershock forecasting system in 

Mexico (which will also be applied in other countries). 

The longstanding cooperation with OFDA has engaged 

USGS scientists countless times to provide expertise 
Appendixes 43

and training, typically in developing countries, many 

of which sit atop the world’s subduction zones. 

• The Nuclear Regulatory Commission (NRC) coordinates with the International Atomic Energy Agency to 

oversee the safety of nuclear plants and to engage in 

response and assessment activities following a nuclear 

incident (such as the meltdown of the Fukushima 

Nuclear Power Station reactors following the 2011 

Tōhoku earthquake and tsunami). Although there are 

no longer U.S. nuclear power plants operating atop 

the most active portion of U.S. subduction zones (the 

Columbia Generating Station in eastern Washington is 

inboard of the Cascade volcanic arc, in the “back-arc” 

region), nuclear power plants along the coasts of the 

Atlantic Ocean, Gulf of Mexico, and California could 

be impacted by tsunami waves generated in subduction 

zones. The NRC recently supported USGS efforts to 

assess the likelihood of tsunamis striking the eastern 

seaboard of the U.S., as a result of local landslide 

sources or earthquakes in the Caribbean (ten Brink and 

others, 2014).

• The Federal Aviation Administration (FAA), within the 

U.S. Department of Transportation, has responsibility 

to issue and disseminate Notices to Airmen (NOTAM) 

when informed of precursory volcanic unrest by USGS 

Volcano Observatories, eruptive activity, or volcanic 

ash in the national air space. 

• The Federal Emergency Management Agency (FEMA) 

is a partner agency with the USGS in the National 

Earthquake Hazard Reduction Program (http://www.

nehrp.gov/). USGS earthquake and tsunami products 

feed directly into FEMA’s software package Hazus 

(https://www.fema.gov/hazus), which estimates potential building and infrastructure losses from earthquakes 

and floods. USGS earthquake data also contribute to 

FEMA’s local hazard mitigation planning tools that 

help communities reduce long-term risk (https://www.

fema.gov/hazard-mitigation-planning-process). Other 

FEMA products, such as flood insurance rate maps 

for the tsunami-vulnerable town of Seaside, Oregon 

(https://catalog.data.gov/dataset/f4100300001d-tiffema-flood-insurance-rate-maps-for-the-seaside-gearhart-oregon-area-gearhart), are built collaboratively 

with USGS and NOAA. Earthquake scenarios and 

subject matter expertise for local to national exercises 

also exemplify the collaboration between the USGS 

and FEMA.

• Other Federal agencies that collaborate with the USGS 

on subduction zone science include the National Institute of Standards and Technology (another partner in 

the National Earthquake Hazard Reduction Program), 

the General Services Administration, the Department 

of Defense, the Department of Energy (DOE), and 

several other Federal agencies that own land, ports, 

buildings, and other structures that are at risk from 

the natural hazards present in subduction zones. For 

example, in a recent assessment, the Government 

Accountability Office mapped the locations of Federal buildings in earthquake-prone areas in the Pacific 

Northwest as part of a Congress-requested assessment of Federal building risk. The DOE operates the 

Hanford Site in Washington, which is the focus of the 

Nation’s largest environmental cleanup project and 

home to the commercially operated Columbia Generating Station nuclear power plant; the USGS and its 

partners operate a seismic monitoring network on and 

around the Hanford Site and conducts geologic field 

studies to assess the seismic hazard associated with the 

multiple faults in the area.

State, Commonwealth, Territorial

State geological surveys, emergency management agencies, insurance organizations, airport authorities, departments 

of transportation, and numerous tribal governing bodies are 

just some examples of State agencies that USGS already 

partners with to assess hazards and distribute information. 

USGS also partners with various entities in the U.S. territories 

of Puerto Rico and the Virgin Islands, Guam, the Mariana 

Islands, and American Samoa.

Professional and Academic Organizations and 

Private Companies

The USGS has a strong tradition of educating and learning through participation in professional societies and consortia concerned with subduction zone geologic processes; for 

example, in the Pacific Northwest these include the Cascadia 

Regional Earthquake Workgroup (http://www.crew.org/), the 

Pacific Northwest Economic Region organization (http://www.

pnwer.org/), and the Western States Seismic Policy Council (http://www.wsspc.org/). By working with engineers in 

academia, private companies, and professional organizations 

(such as the Applied Technology Council, Earthquake Engineering Research Institute, Structural Engineers Association of 

Washington, Pacific Earthquake Engineering Research Center, 

Center for Disaster and Risk Analysis), USGS scientists 

ensure that its products are useful to as many communities 

as possible. 
44 Reducing Risk Where Tectonic Plates Collide—A Plan to Advance Subduction Zone Science

Monitoring Networks

Large-scale, permanent monitoring networks are often 

operated as partnerships between the USGS and other institutions and data are publicly shared. Seismic networks on 

U.S. subduction zones include the Northern California Seismic 

Network (jointly operated by the USGS and the University of 

California, Berkeley), the Pacific Northwest Seismic Network 

and Cascade Chain Volcano Monitoring Network (with the 

University of Washington), the Alaska Earthquake Information Center and the Alaska Volcano Observatory (with the 

University of Alaska, Fairbanks), the Puerto Rico Seismic 

Network (with the University of Puerto Rico), and the Canadian National Seismograph Network (with Natural Resources 

Canada). For monitoring slower deformation, mainly using 

GPS, networks operated by the USGS and partners include the 

Pacific Northwest Geodetic Array (with Central Washington 

University) and volcano-specific sites operated by the California, Cascades, and Alaska Volcano Observatories (which 

are mainly maintained by the USGS). These and other GPS 

networks contribute data to the much larger Plate Boundary 

Observatory (PBO, which has 1,100 sites), a major component 

of NSF’s EarthScope Program; data from EarthScope have 

contributed to many USGS subduction zone studies and will 

be employed in the USGS’s earthquake early warning system. 

Currently, the PBO has a scheduled termination date in 2018, 

but NSF is considering a follow-on National Geophysical 

Observatory for Geoscience. Such an observatory would allow 

for continued operation of the current Seismological Facilities 

for the Advancement of Geosciences (SAGE) and Geodesy 

Advancing Geosciences and EarthScope (GAGE) facilities. 

The USGS also uses data from satellites, including radar 

instruments operated cooperatively by several governments, 

including the European Union, South Korea, and Japan.

Offshore Facilities

For U.S. oceanographic vessels and instrumentation, the University-National Oceanographic Laboratory 

System (UNOLS) coordinates U.S. ship schedules and the 

NSF-supported Ocean Bottom Seismograph Pool (OBSIP), 

which is a distributed oceanographic instrument pool; the 

USGS has collaborated with both of these groups to carry out 

experiments in multiple subduction zones. The International 

Ocean Discovery Program (IODP) organizes scientific drilling 

expeditions in ocean basins to acquire samples and measurements that address a wide range scientific questions. IODP 

experiments are planned years in advance; recent and upcoming expeditions relevant to subduction zone science include 

cruises to Sumatra (2016), the Mariana subduction zone 

(2016–2017), and New Zealand (2017 and 2018). A recent 

major IODP effort has been to drill into and instrument the 

earthquake-generating fault of the Nankai Trough subduction 

zone offshore Japan (NanTroSEIZE); future IODP cruises may 

include similar efforts in the U.S subduction zones of Cascadia, the Alaska-Aleutian Trench, and the Mariana Islands.

The U.S. Geological Survey and the University of 

Alaska, Fairbanks, partner to monitor earthquakes on 

and around significant infrastructure, such as at this 

dam at Bradley Lake, which is the largest hydropower 

project in Alaska. Photograph by Ian Dickson, Alaska 

Earthquake Center, University of Alaska, Fairbanks.
Appendixes 45

Appendix 2. International Monitoring, Disaster Mitigation and Response, and 

Capacity Building

As a global leader in Earth science research, the USGS 

has a long history of collaboration with foreign scientists, 

agencies, and governments to provide information and guide 

best practices before, during, and after natural disasters, particularly in subduction zones. In this appendix we summarize 

some of these international collaborations. 

The U.S. Geological Survey (USGS) National Earthquake Information Center (NEIC) determines, as rapidly and 

accurately as possible, characteristics and potential effects 

of earthquakes that occur worldwide. It disseminates this 

information within minutes to National and international 

agencies, scientists, critical facilities, and the general public. 

The Global Seismograph Network (GSN; https://www.iris.

edu/hq/programs/gsn) is a cooperative partnership involving 

the Incorporated Research Institute for Seismology (IRIS), 

the National Science Foundation and the USGS. It provides 

free, real-time, open-access seismological data from more 

than 150 stations worldwide. Since the early 1990s, Japan, 

New Zealand, and Canada have been monitoring portions of 

their subduction zones and many of their hazardous volcanoes 

using both onshore and offshore geophysical instruments. 

Geodetic instrumentation to track plate motion in Chile, 

Mexico, and the Caribbean is being deployed with the aid of 

funding from government agencies in other nations, including 

the United States.

Through a multinantional agreement called the International Charter: Space and Major Disasters, the USGS and 

other member agencies contribute satellite imagery in support 

of disaster response. The Volcano Disaster Assistance Program 

(VDAP) is a global volcanic risk mitigation activity that is 

co-funded by the U.S. Agency for International Development (USAID) and the USGS. The more recently established 

USGS/USAID Earthquake Disaster Assistance Team (EDAT)

provides technical assistance to establish monitoring capabilities, collect relevant geologic field data, conduct geophysical 

surveys, and more, collaborating with local scientists shortly 

after large earthquakes occur in foreign countries so that 

they can “build back better” after events. EDAT has supported activities in a number of countries with subduction 

zone settings.

USGS scientists contribute research results to a wide 

range of international organizations focused on mitigating 

tsunami hazards. The Intergovernmental Oceanographic Commission (IOC) Tsunami Programme (http://www.ioc-tsunami.

org/index.php?option=com_content&view=article&id=1&It

emid=2&lang=en) supports member States in assessing tsunami risk, implementing tsunami early warning systems, and 

educating communities at risk about preparedness measures. 

These missions are addressed by the IOC through actions of 

the International Tsunami Information Centre (ITIC), which 

it oversees. The ITIC is a professional interchange, supported 

by the United Nations Educational, Scientific and Cultural 

Organization (UNESCO) and the National Oceanic and Atmospheric Administration (NOAA), that maintains relationships 

with scientific organizations, civil defense agencies, and the 

general public. The NOAA Pacific Tsunami Warning Center 

(http://ptwc.weather.gov/ptwc/responsibilities.php) provides 

warnings for Pacific Ocean tsunamis to the countries around 

the Pacific Rim and the Pacific island states with U.S. interests, under the auspices of UNESCO. NOAA also operates the 

National Tsunami Warning Center (http://wcatwc.arh.noaa.

gov/), which serves the continental United States, Alaska, 

Puerto Rico, the Virgin Islands, and Canada.

The International Civil Aviation Organization (ICAO) 

has established nine Volcanic Ash Advisory Centers (VAACs, 

http://vaac.arh.noaa.gov) across the world to keep aviators 

informed of volcanic hazards. The USGS hosts the website for 

the Volcanic Ashfall Impacts Working Group, an international 

consortium of multidisciplinary geoscientists focused on ashcloud forecasting and understanding and mitigating the effects 

of ashfall.

USGS partnerships with the private sector include the 

many corporations that have facilities, financial institutions that have investments, and insurers that have clients in 

subduction zones globally. Additionally, private, non-profit, 

and governmental international aid organizations, such as the 

International Red Cross, Oxfam, and various assistance arms 

of the United Nations, require information about subduction 

zone hazard and risk. The Global Earthquake Model (GEM; 

https://www.globalquakemodel.org) is a public-private partnership that guides and funds work such as urban risk scenario 

development and experimental risk reduction initiatives. The 

Global Volcano Model (GVM; http://globalvolcanomodel.

org) is an international effort to create an accessible information platform that models volcanic hazard and risk on global 

and regional scales, and to support volcano observatories at 

a local scale. Both GEM and GVM count risk-modeling and 

reinsurance companies among their sponsors. A more nascent, 

comparable effort to develop a Global Tsunami Model also 

is underway.
Publishing support provided by: 

Menlo Park, California, and Rolla, Missouri, Publishing Service Centers

Manuscript approved for publication March 24, 2017 

Edited by Claire M. Landowski 

Layout and design by Suzanne Roberts

For more information concerning this publication, contact: 

USGS Earthquake Science Center 

345 Middlefield Road 

Mail Stop 977 

Menlo Park, CA 94025 

(650) 329-4668

Or visit the USGS Earthquake Science Center Web site at: 

https://earthquake.usgs.gov/contactus/menlo/
Back cover. GPS (Global Positioning System) data, such as from a station near Iniskin Bay, 

Alaska, provide key constraints on the characteristics of individual earthquakes and their impacts. 

This station contributed important information following the damaging magnitude 7.1 Iniskin 

earthquake near Anchorage, Alaska, in 2016. Maintenance of these remote sites require support 

from ships and helicopters, as shown here. Photograph by Heidi Willoughby, UNAVCO.
Gomberg and others—Reducing Risk Where Tectonic Plates Collide—A Plan to Advance Subduction Zone Science—Circular 1428

ISSN 1067-084X (print) 

ISSN 2330-5703 (online)

https://doi.org/10.3133/cir1428