Open-File Report 2011–1101

Prepared under United States Nuclear Regulatory Commission-United States

Geological Survey Interagency Agreement JCN-N6184—Assessment of the 

Current State of the Advanced National Seismic System

Improved Earthquake Monitoring in the Central

and Eastern United States in Support of 

Seismic Assessments for Critical Facilities

U.S. Department of the Interior

U.S. Geological Survey
Prepared under United States Nuclear Regulatory Commission-United States 

Geological Survey Interagency Agreement JCN-N6184—Assessment of the 

Current State of the Advanced National Seismic System 

Improved Earthquake Monitoring in the Central and 

Eastern United States in Support of Seismic 

Assessments for Critical Facilities 

By William S. Leith, Harley M. Benz, and Robert B. Herrmann 

Open-File Report 2011–1101

U.S. Department of the Interior 

U.S. Geological Survey 
ii

U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2011

For product and ordering information:

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Suggested citation:

Leith, W.S., Benz, H.M., and Herrmann, R.B., 2011, Improved earthquake monitoring in the central 

and eastern United States in support of seismic assessments for critical facilities: U.S. Geological 

Survey Open-File Report 2011–1101, 29 p.

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

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report.

ShakeCast/ShakeMap software uses Google, Inc., imagery as a base for presentation of seismic 

information. Image copyright remains with Google, Inc.
iii

Contents

Introduction ............................................................................................................................................. 1

Augmentations to Regional Seismic Networks and the Advanced National Seismic System.................. 2

Coordinated Station Upgrades and Infrastructure Improvements for Seismic Monitoring ................... 2

Improved Near-Source Monitoring through Coordinated Upgrades of Existing Seismographic 

Stations and Infrastructure through the American Recovery and Reinvestment Act ........................... 3

Seismic Hazard in the Northeastern United States.............................................................................. 4

Seismic Hazard in the Southeastern United States ............................................................................. 5

Seismic Hazard in the Central United States....................................................................................... 7

Recent Improvements to the Advanced National Seismic System and Regional Seismic Networks ... 7

Augmentation of Seismic Networks to Support Critical Facilities Requirements................................ 10

Potential Strong-Motion Recording Options ...................................................................................... 13

Justification for Enhanced Monitoring—Case Studies in Oklahoma and Illinois ................................ 14

Oklahoma Case Study: 2009–2010 Oklahoma Earthquake Swarm Northeast of Oklahoma City.. 14

Illinois Case Study: February 10, 2010, M 3.8 Northern Illinois Earthquake .................................. 17

Future Improvements to Advanced National Seismic System and Regional Seismic Networks........ 21

Development of Rapid Delivery of Parametric Ground-Motion Data.................................................. 21

Summary............................................................................................................................................... 26

Acknowledgments................................................................................................................................. 27

Contributors .......................................................................................................................................... 28

Selected References............................................................................................................................. 29

Figures

1. Map showing probabilistic seismic hazards for the central and eastern United States

with locations of existing Advanced National Seismic System stations and nuclear powerplant

locations....... ...................................................................................................................................4

2. Map showing seismic broadband and strong-motion stations in the eastern

United States slated to be upgraded under the American Recovery and Reinvestment Act ............6

3. Map illustrating existing seismic stations in the central United States including

stations to be upgraded under the American Recovery and Reinvestment Act ................................8

4. Map of existing seismic stations in the central and eastern United States and planned upgrades 

under the American Recovery and Reinvestment Act .................................................................... 12

5. Summary map of relative earthquake locations near Oklahoma City, Oklahoma, 

January and February 2010, using existing stations, the Transportable Array, and temporary 

NetQuakes strong-motion recorders............................................................................................... 15

6. Seismograms and regional moment tensor results from the February 2010 M 3.2

Oklahoma earthquakes.................................................................................................................. 16

7. Map showing location of the February 2010 northern Illinois earthquake, nuclear plants, and 

seismic stations of the Advanced National Seismic System........................................................... 18

8. Map showing macroseismic intensities near Elgin, Illinois, from the February 2010 earthquake, 

from web-based entries .................................................................................................................. 19

9. Example ShakeCast output showing seismic intensities from the February 2010

earthquake at near-field nuclear plants, Illinois............................................................................... 20
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10. Overview of the ShakeCast system for quantifying and displaying earthquake

ground-shaking information, from the user’s perspective ............................................................... 22

11. Example of ShakeCast information delivery from the M 7.8 San Andreas scenario earthquake.... 24

Table

1. Table showing generic description of strong-motion system options.............................................. 13

Abbreviations

ANSS Advanced National Seismic System

ARRA American Recovery and Reinvestment Act

CERI Center for Earthquake Research and Information, University of Memphis

CEUS Central and eastern United States

ENS Earthquake Notification System (ANSS product)

FEMA Federal Emergency Management Agency

IRIS Incorporated Research Institutions for Seismology

NEHRP National Earthquake Hazards Reduction Program, U.S. Geological Survey

NEIC National Earthquake Information Center, U.S. Geological Survey 

NSHM National Seismic Hazard Maps, U.S. Geological Survey

RSNs Regional Seismic Networks

TA Transportable Array of EarthScope (National Science Foundation and IRIS)

USGS U.S. Geological Survey

USNRC U.S. Nuclear Regulatory Commission

CISN–Display California Integrated Seismic Network–Display (ANSS product)
1

Improved Earthquake Monitoring in the Central and 

Eastern United States in Support of Seismic 

Assessments for Critical Facilities

By William S. Leith, Harley M. Benz, and Robert B. Herrmann

Introduction

This report was developed in response to a request by the U.S. Nuclear Regulatory 

Commission (USNRC) for evaluation of seismic monitoring capabilities in the central and eastern 

United States (abbreviated in this report as CEUS) with an emphasis on meeting current and future 

needs of the USNRC. This ―Phase II‖ report focuses on specific improvements to earthquake 

monitoring in the CEUS likely to further the USNRC’s goals for improved understanding of seismic 

hazards within this region.

This report is not an assessment of the seismic safety of nuclear powerplants (NPPs) in the 

CEUS. The USNRC is responsible for assessing the seismic safety of individual NPP’s, but based 

on specific seismic and engineering information not considered in this report.

To accomplish this evaluation task, the report provides an update on the current state of 

earthquake monitoring in the CEUS, a description of seismic upgrades in the CEUS supported by 

the U.S. Geological Survey through the American Recovery and Reinvestment Act (ARRA) of 

2009, and proposals for deployment of new instrumentation. The report also proposes the adoption 

of earthquake notification and emergency response tools using Advanced National Seismic System 

(ANSS) earthquake information and products that show the distribution of ground shaking from 

significant earthquakes. The assessment and findings in this report, developed herein at the request 

of the NRC, would also benefit other federal and state entities with responsibility for critical 

infrastructure in the region.

Enhancements in earthquake monitoring in the CEUS which could result in an improved 

understanding of seismic hazards and improved situational awareness after earthquakes are as 

follows:

38 new Advanced National Seismic System strong-motion stations in active CEUS earthquake 

source zones to improve seismic monitoring infrastructure for response, assessment and 

mitigation;

62 new strong-motion stations near nuclear powerplants to record near-nuclear-plant ground 

shaking;

expanded databases of strong ground-motion data and Green’s Function data for earthquake 

source characterization, attenuation, and propagation across the CEUS; and

improved ShakeMap and ShakeCast tools at the USNRC and other state and Federal users for 

rapid response and assessment activities.

Numerous strategies exist for improved seismic monitoring throughout the region, each with 

associated trade-offs and costs. For example, comprehensive seismic monitoring throughout the 

region comparable to that found in California (which is broadly monitored at magnitude threshold 
2

of M 1.8–2.0) would require hundreds of new stations, capitalization costs in the tens of millions of 

dollars, and associated long-term operation and maintenance costs in the millions of dollars. Over 

the long term, such a network would guarantee seismic catalog completeness to lower magnitudes 

(likely less than M 2), accurate earthquake locations (in the range ± 1–2 kilometers, km), improved 

understanding of seismotectonics, and better models of near-source and regional attenuation.

Recognizing that dense, permanent deployments of new stations throughout the CEUS are 

not likely, a pragmatic approach utilizes augmentation of existing deployments to ensure better 

characterization of the seismotectonics of notable seismic source zones in the CEUS. Such 

augmentation would improve quantification of near-source attenuation in regions where larger 

earthquakes are expected, as well as support systematic collection of data and observations from 

existing permanent and temporary networks, ultimately to improve estimates of earthquake source 

parameters, attenuation, and propagation. While this approach costs less to implement and operate 

than does the dense-deployment approach, it requires careful modeling and calibration efforts to 

improve determination of earthquake locations for larger events (those typically greater than M 2.5–

3.0) and limits catalog completeness to a higher threshold (that is, M 2.5 or larger). Augmentation, 

however, will provide limited near-source data for the rare event that is outside of the more densely 

monitored source zones.

Knowing that it operates limited seismic monitoring assets in the CEUS, the U.S. Geological 

Survey has begun development of modeling procedures and processing algorithms to leverage 

unique capabilities of the Transportable Array and the upgraded Advanced National Seismic 

System stations to better calibrate source and path effects. The EarthScope Transportable Array 

(funded by the National Science Foundation and implemented by the IRIS Consortium) is an 

approximately 400-station network that is rolling across the country collecting continuous seismic 

data for approximately 18 months at each site. When completed, the Transportable Array will 

provide temporary, but uniform, coverage of the continental United States with an interstation 

spacing of about 70 km.

Many of the determinations in this report are based on the assumption that active research 

and development within the USGS National Earthquake Hazards Reduction Program and leveraged 

results and products from the Transportable Array together provide new capabilities using existing 

and augmented systems to address hazards of interest to both the U.S. Geological Survey and to the 

U.S. Nuclear Regulatory Commission, as well as to other state and Federal agencies.

Augmentations to Regional Seismic Networks and the Advanced National 

Seismic System

Coordinated Station Upgrades and Infrastructure Improvements for Seismic Monitoring

Both the U.S. Geological Survey (USGS) and the U.S. Nuclear Regulatory Commission 

(USNRC) have an interest in improved seismic monitoring across the United States, particularly for 

hazard mitigation and response. The USGS and USNRC perform complementary missions of 

addressing earthquake hazards that lead to efficient and effective damage- and loss-mitigation 

policies. The American Recovery and Reinvestment (ARRA) Act of 2009 provided a rare 

opportunity to coordinate upgrades of seismographic stations to achieve objectives of better 

acquisition and processing of seismic data of engineering interest, better constraints on earthquake 

source parameters (location, magnitude, and style of faulting) used in assessment and mitigation 

activities, and better dissemination of earthquake information to assist in post-earthquake response 

and recovery activities.
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Given the areal distribution of seismic source zones and limited deployment of stations within 

active earthquake source zones, seismic monitoring capabilities vary considerably across the CEUS. 

Identification and characterization of seismically active structures are important input for the USGS 

National Seismic Hazard Maps (NSHM) and also are a requirement for site-specific seismic-hazard 

analyses for most critical structures, including nuclear powerplants. To better characterize seismic 

source zones, accurate locations (within 1–2 km or less) for all earthquakes down to the smallest 

practical magnitude is desired, since spatial seismicity trends may be an important indicator of the 

location of seismically active geologic structures. Overall, regional seismic networks (RSNs) in the 

CEUS do an adequate job of documenting earthquake source parameters across the region as a whole 

and a good job in selected source regions (for example, the New Madrid seismic zone), which reflects

traditional USGS hazard-mitigation priorities. For development of the NSHMs, earthquake-data 

completeness for the CEUS down to M 3.0–3.5 is needed with an epicentral accuracy of about 3–5 km. 

On the other hand, however, site-specific seismic hazard studies at a critical facility, such as a nuclear 

powerplant (NPP), might require a complete database of earthquakes within 200 km of the site down to 

M 2.0 or lower to support the most robust estimates possible of local seismicity rates and to provide the 

largest possible dataset for identifying potentially active structures. Through the ARRA project, the 

USGS has tried to balance the need to target upgrades in areas of highest seismic hazard (such as eastern 

Tennessee, upstate New York, and the New Madrid zone) while also improving areal monitoring to 

assist USNRC in its broader earthquake assessment and mitigation activities. 

Improved Near-Source Monitoring through Coordinated Upgrades of Existing Seismographic 

Stations and Infrastructure through the American Recovery and Reinvestment Act 

On the basis of geological and geodetic constraints, such as seismicity, probabilistic seismic 

hazard maps (fig. 1) highlight those areas of the CEUS that have a high likelihood of experiencing 

significant ground motions during the nominal 20-year lifetime of any seismic instrumentation. 

Strategically deployed seismographic stations in critical areas provide essential data that can be used to 

better characterize the seismotectonics of active CEUS source zones through better constraints on 

earthquake source properties (for example, depth, moment-magnitude, or mechanism) critical in 

improving earthquake ground-motion scaling relations and attenuation models. 

A plot of existing seismic stations and NPPs on the probabilistic NSHM of the United States 

(fig. 1) provides a framework for understanding the present state of monitoring. It also provides a basis 

for identifying gaps in monitoring capabilities. The distribution of seismic stations in the CEUS shows a 

two-tiered approach to monitoring (fig. 1). Throughout the United States there is a uniform deployment 

of widely spaced broadband/strong-motion stations that makes up the ANSS backbone network. Each of 

these stations is capable of recording at 200 samples per second and up to ±2 g of acceleration. The 

backbone network guarantees uniform monitoring of the continental United States to a level of about M 

3 with location errors within 5–10 km and magnitude uncertainties of ±0.2 magnitude units. This 

network complements denser networks of stations in selected seismic source zones (for example, eastern 

Tennessee, upstate New York, and the New Madrid Fault Zone) with lower detection thresholds, 

typically below M 2. These dense networks of stations provide detailed information on earthquake 

source characteristics for seismic source zones of interest to the USGS National Earthquake Hazards 

Reduction Program and State monitoring programs (for example, that of the State of Tennessee). 

Although the USGS and its monitoring partners try to place seismograph stations in most of the 

expected source zones, many of these source zones are inadequately monitored in terms of catalog 

completeness to low magnitudes, earthquake location accuracy, and on-scale ground motion recordings 

for earthquakes of engineering interest. Many such high-gain, short-period stations cannot stay on-scale 

for events larger than approximately M 3.0 at distances less than 100–150 km. 
4

Figure 1. Map showing probabilistic seismic hazards (0.1 g in 50 years) for the central and eastern 

United States with locations of existing Advanced National Seismic System stations and nuclear 

powerplant locations.

Seismic Hazard in the Northeastern United States

In the northeastern United States, the seismic hazard is dominated by seismic activity 

associated with the St. Lawrence rift zone, which has produced some of the largest eastern North 

American earthquakes (for example, eastern Canada earthquakes of note include the 1925 M 6.2 

Charlevoix, 1988 M 5.9 Saguenay, and 1944 M 5.6 Cornwall, Canada, and Massena, New York,

earthquakes). Seismic activity in or near the St. Lawrence rift zone is seen as the highest hazard 
5

region in upstate New York and northern Maine. Historically, there have been significant 

earthquakes elsewhere in the northeastern United States, with notable events in western New York, 

Massachusetts, New Jersey, Pennsylvania, Ohio, and Maine. The two largest earthquakes reported 

in the northeast were the M 6+ earthquake of 1638 (central New Hampshire) and the 1755 

earthquake offshore Massachusetts, near Cape Ann. In the 20th century, there have been a number of 

earthquakes in the M 5 range in upstate New York, Maine, and Pennsylvania. 

Because of the lack of well-defined seismic source zones in the northeastern United States, a

major goal of seismic monitoring is to capture on-scale strong ground-motion records in near-source 

regions and urban environments that are at risk to rare but significant earthquakes. Consequently, 

seismographic stations are deployed in and around upstate New York and near the metropolitan 

areas of New York and Boston, with more widely spaced stations in Pennsylvania, New York, and 

New England. Earthquake source zones that remain sparsely monitored include northern-most 

Maine, northeastern Ohio, western Pennsylvania, and western and upstate New York.

Seismic Hazard in the Southeastern United States

The southeastern United States contains at least two seismic zones of elevated hazard: the 

Charleston, South Carolina, zone and the eastern Tennessee zone. The Charleston Seismic Zone 

(CSZ), sometimes also called the Middleton Place–Summerville Seismic Zone, is the source of 

the largest historically documented earthquake in the CEUS after the New Madrid sequence of 

1811–1812: the M 7+ earthquake near Charleston in 1886. The historic record contains many 

other large felt earthquakes and widespread paleoseismic and paleoliquifaction data that suggest 

prehistoric levels of shaking sufficient to produce nonlinear site responses about every 500 years 

over the last 6,000 years. Elevated levels of hazard with a 10 percent probability of shaking in the 

0.02–0.04 g range span nearly the entire state of South Carolina, for example. Current monitoring 

in the CSZ (fig. 2) consists of three broadband and three digital short-period stations together with 

four free-field strong-motion stations operating in near-real-time in the Charleston/Summerville 

metropolitan area. 

The East Tennessee Seismic Zone (ETSZ) is the second most active zone in the CEUS and 

covers a 100- by 300-mile swath across northeastern Alabama, northwestern Georgia, eastern 

Tennessee, western North Carolina, southeastern Kentucky, and southwestern Virginia (fig. 1). The 

largest instrumentally recorded earthquakes in the region were the April 29, 2003, M 4.6 near Fort 

Payne, Alabama, and the November 30, 1973, M 4.6 earthquake south of Knoxville, Tennessee. 

Paleoseismic evidence for large historical earthquakes has not been developed as yet. Seismogenic 

depths within the ETSZ typically are 5–22 km, with most events occurring on steeply dipping faults 

beneath a Paleozoic décollement, a large-scale shallow-angle fault or shear zone. Focal mechanisms 

are remarkably consistent along the entire length of the zone and suggest strike-slip motion on an 

organized set of basement faults. Current monitoring in the ETSZ is accomplished with a network 

of 23 three-component analog short-period (SP) stations (at about 25-km interstation spacing), three 

three-component broadband stations, and three three-component free-field strong-motion stations 

(fig. 2). While relatively dense in terms of total instrumentation, the analog SP stations will clip for 

earthquakes larger than about M 2–2.5 within the ETSZ. 
6

Figure 2. Map showing seismic broadband and strong-motion stations (outlined with magenta symbols) in the eastern United States slated to 

be upgraded under the American Recovery and Reinvestment Act (ARRA). The ARRA upgrades include both broadband plus strong-motion 

sites (triangles) and short-period plus strong-motion sites (plus signs).
7

Seismic Hazard in the Central United States

The seismic hazard in the central United States (fig. 1) is spatially distributed, with 

major seismic source zones of elevated hazard in and around the New Madrid Seismic Zone 

in southeastern Missouri and adjacent parts of Illinois, Kentucky, Tennessee, and Arkansas, 

and in the Wabash Valley Seismic Zone in Indiana and Illinois. The New Madrid and 

Wabash Valley Seismic Zones are roughly contiguous and stand out on probabilistic seismic 

hazard maps as a region of high likelihood for exceeding 0.1 g in a 50-year-period (fig. 1). 

The New Madrid zone produced three powerful earthquakes between M 7.0–8.0 in 

1811–12, as well as previous sequences of large earthquakes in about 1450 and 900 A.D.,

documented by paleoliquefaction evidence. The narrow, approximately 500 km-long zone 

between Marked Tree, Arkansas, and Mt. Carmel, Illinois, has seen about 25 M >4 

earthquakes in the last 50 years. Although the probability of observing 0.1 g at any given 

location along this zone is only about 2 percent annually, the aggregate likelihood of 

observing 0.1 g somewhere in this zone is much higher.

While the current distribution of upgraded broadband seismographs and 

accelerographs in the most active portion of the NMSZ yields station spacing of about 25 km 

(fig. 3), the larger area likely to experience strong shaking has average station separation of 

about 50–100 km. That network is too sparse to capture on-scale the necessary near-source 

ground-motions, to constrain closely hypocenters, or to resolve amplitude-versus-distance 

scaling issues. This report will address the need for instruments capable of on-scale recording 

within 50 km of expected earthquake sources.

Recent Improvements to the Advanced National Seismic System and Regional Seismic 

Networks

The American Recovery and Reinvestment Act (ARRA) funding has been used by 

the USGS to upgrade the ANSS backbone network and regional seismic networks (RSNs) to 

ensure region-wide monitoring at high fidelity. In addition, the USGS provided ARRA 

money to the University of Memphis, Saint Louis University, Weston Observatory of Boston 

College, and the Lamont-Doherty Earth Observatory of Columbia University to upgrade their 

regional broadband stations to newer and quieter broadband sensors and to add three 

channels of strong-motion data to each station. Some short-period stations in higher-hazard 

source zones (for example, upstate New York and the ETSZ) also are being upgraded to 

include strong-motion sensors (figs. 2 and 3).

Through the ARRA, the USGS is making a major investment in seismic monitoring 

in the CEUS. A total of 80 existing seismic stations in the region will be upgraded to modern 

ANSS standards of high-dynamic-range recording of low-noise accelerometers and either 

low-noise broadband or short-period sensors. In addition, the USGS is upgrading the regional 

network operation centers to ensure comprehensive cataloging of ground-motion data and 

earthquake source parameters using well-defined standards of data exchange and processing 

and descriptions of instrument response. When completed by the end of calendar year 2011, 

such upgrades will improve significantly the ability of ANSS to record ground-motion data 

for M 3 and larger earthquakes of engineering interest within some of the key CEUS active 

source zones. 
8

Figure 3. Map of existing seismic stations in the central United States and planned station upgrades under American Recovery and 

Reinvestment Act. Stations outlined with pink symbols identify stations slated for upgrades.
9

The National Science Foundation (NSF)-sponsored EarthScope project also plays a 

significant role in improving seismic monitoring of the CEUS. As part of EarthScope, IRIS 

has deployed a 400-station temporary array of broadband stations called the Transportable 

Array (TA) that is rolling across the United States. (The rearmost station is moved to the lead 

position as the array ―rolls‖ from west to east.) Each station is operated for 18–24 months 

before being moved to a new location along the traverse. Interstation spacing for this moving 

network is approximately 70 km. By providing uniform sampling across the continental 

United States, the TA network will enable the USGS and USNRC to ―calibrate‖ crustal 

structure, which has implications for improved earthquake-location determinations and 

synthetic seismogram calculations used in moment-tensor descriptions of earthquakes. In 

addition, as the TA rolls across the country, the USGS and USNRC have an opportunity to 

evaluate individual stations for adoption into existing network operations in order to add 

them as permanent stations and improve overall network capabilities.

Suggested research and development activities involving coordination of USGS, 

USNRC and university scientists include:

Work with the Department of Energy (DOE) national laboratories and through the 

National Earthquake Hazards Research Program (NEHRP) external grants program to use 

the TA data and ground-truth events to improve estimates of velocity structure needed in 

routine location and waveform-modeling procedures.

Collect accurate interstation Green’s Function data that can be used in a variety of 

standard and novel modeling procedures better to determine earthquake epicenters, 

depths, and moment-tensor parameters without the need for costly expansion of stations 

outside the expected areas of activity.

Supplement United States ground-motion datasets with strong-motion data along the 

United States-Canada border from Canadian stations integrated into ANSS operations.

Establish an ad-hoc advisory committee of USGS and USNRC personnel to prioritize 

seismic-monitoring research and development efforts in the CEUS using existing funding 

structures such as specific elements of the NEHRP external grants program.

Develop with the RSNs evaluation criteria and procedures to identify key TA stations 

that could be adopted as part of a long-term monitoring strategy.

Activities that are underway or are being considered to address some of these research and 

development efforts include:

Department of Energy (DOE) national laboratories are developing improved velocity 

models of the United States for explosion monitoring and verification as part of the 

United States-supported Comprehensive Test Ban Treaty augmentation. The USGS 

National Earthquake Information Center has provided Lawrence Livermore National 

Laboratory well-documented ground-truth events for the continental United States, which

are necessary to calibrate such continental-scale velocity models. It is expected that such

calibration efforts will reduce location biases/errors by at least a factor of 2.

The USGS is supporting a two-year Mendenhall postdoctoral fellowship to investigate 

new approaches for use of interstation Green’s Function data derived from ambient-noise 

data under a primary focus of addressing issues related to three-dimensional basin and 

regional effects on seismic ground motions. The USGS also is investigating new location 

procedures using interstation Green’s Function data derived from both the TA network 

and existing ANSS stations.
10

The USGS Geologic Hazards Science Center systematically is storing all such 

interstation Green’s Functions derived from USGS studies for easy access in future 

seismic ground-motion studies, computation of improved crust and upper-mantle velocity 

models, and improved estimations of source parameters.

The USGS National Earthquake Information Center (NEIC) presently is acquiring data 

from Geological Survey of Canada (GSC) strong-motion stations from Haiti in real-time.

The USGS has developed procedures to automatically extract ground-motion parameters 

of engineering interest from both broadband and strong-motion time-series data for use 

by the USGS National Strong Motion Project.

The State of Arkansas is adopting six TA stations with USGS funding. Consequently, the 

University of Arkansas/Little Rock, CERI (the University of Memphis Center for 

Earthquake Research and Information), and the USGS are working together to ensure that 

adopted stations meet minimum performance standards and address regional monitoring 

and hazards issues. The effort could be considered a pilot for developing a process for 

strategic adoption of other TA stations in the CEUS.

These efforts leverage the ARRA upgrades to existing networks, recognize the importance of 

EarthScope Transportable Array deployment to improve models and modeling procedures, 

and use existing USGS research activities and staff to facilitate the research and development 

needed to provide new and more accurate monitoring products.

Augmentation of Seismic Networks to Support Critical Facilities Requirements

Detailed hazard assessments at nuclear powerplants in the CEUS are based on models 

of earthquake ground motions for moderate and large earthquakes largely derived from 

recordings of small earthquakes (M <5) in the CEUS. The primary sources of data for such 

assessments come from USGS-supported or -operated seismic networks. The uncertainty in 

ground-motion prediction models is one of the largest sources of total uncertainty in 

probabilistic seismic hazard results. In order to reduce this component of uncertainty in 

hazard assessments, it is appropriate to consider potential improvements in the groundmotion and source-parameter database of small and moderate earthquakes in the CEUS 

through strategic deployment of stations in selected seismic source regions and in the vicinity 

of critical facilities.

Because the USGS and its regional partners operate broad-based seismic monitoring 

networks in the CEUS, adding new stations to existing monitoring systems is relatively easy 

and cost-effective and carries a high probability of success. The USGS National Earthquake 

Information Center and RSNs in the CEUS easily can handle new stations and integrate 

resulting data into existing processing algorithms to produce timely and accurate earthquake 

information products tailored to meet specific agency mission requirements. Additionally, the 

Advanced National Seismic System (ANSS) has established standards for all aspects of its 

monitoring efforts (including, for example, instrumentation standards, station metadata 

standards, and data-exchange protocols and formats). Considering all of these factors, it is 

cost-effective for the USGS or other funding partners to collaborate on improved seismic 

monitoring in the CEUS through upgrades of existing sensor systems or installation of new 

stations where recognized deficiencies in coverage appear. Ultimately, targeted upgrades 

integrated into existing processing systems improve general and task-specific performance, 

which in turn reduces uncertainty in hazard estimates for low-probability events and provides 

more confidence in seismic design.
11

To improve the strong-motion database of earthquakes in the CEUS, it is important 

that the number of operating strong-motion stations be increased throughout the region to 

ensure capture of infrequent earthquakes of engineering interest. Figure 4 indicates locations 

of existing seismic stations operated by the USGS and RSNs, along with suggested upgrades 

and additions of new stations. In order to address the need to compute accurately earthquake 

source parameters and to understand site response and propagation effects at or near NPPs or 

other critical facilities, the USGS suggests upgrading or installing an additional 100 stations. 

Some of those new or upgraded stations are targeted at under-instrumented earthquake source 

regions; others are sited near critical facilities. Both sets of instrumentation will improve 

estimates of source parameters, increase understanding of propagation and attenuation 

relationships across the region, and enhance understanding of site-specific assessments at 

each of the critical facilities.

In many parts of the CEUS, especially the northeastern and southeastern United 

States, the density of seismic stations is not sufficient to achieve optimum monitoring for 

site-specific seismic hazard studies. To provide accurate hypocentral determinations for 

earthquakes down to M 2.0, for example, four to six seismic stations at hypocentral distances 

less than 50–150 km surrounding expected earthquakes are necessary. In addition, bettercalibrated velocity models for the CEUS should be developed. Consequently, the USGS and 

RSNs have identified 38 new or potential upgraded strong-motion sites (blue squares in 

fig. 4) in seismic source zones that are not adequately monitored at present (meaning either 

no stations within about 50 km, or existing stations which cannot remain on-scale for 

anticipated seismicity occurring within 50 km). The majority of these stations either augment 

existing networks (for example, in the New Madrid Seismic Zone or the Eastern Tennessee 

Seismic Zone) or provide new monitoring capabilities where none existed before (such as in 

central Oklahoma or in the Rio Grande Rift of north-central New Mexico). In some areas, 

such as western Colorado, existing short-period/broad-band networks currently are used for 

basic monitoring, but additional or upgraded stations are needed to ensure high-quality 

ground-motion recording within 50 km of a potential moderate to large earthquake.

In addition to deployment of 38 strong-motion stations to improve the performance of 

seismic monitoring installations across the region, the USGS suggests deployment of 62 new 

real-time strong-motion stations near or at critical facilities sites in the CEUS. Many of the 

proposed stations fall outside an ANSS deployment strategy (that is, upgrading and 

increasing the numbers of stations within CEUS active seismic-source zones of interest to the 

USGS Earthquake Hazards Program). In some cases, critical facilities are within or near 

active source zones (for example, the Eastern Tennessee Seismic Zone and the Charleston

Seismic Zone), and any upgrades near those facilities would perform a dual purpose of better 

characterization of earthquake source parameters and near-facilities site effects. Installation 

of new strong-motion stations at or near other critical facilities mainly would be used for 

evaluation of site response and regional propagation issues and additionally would be used in 

emergency-response applications like ShakeMap and ShakeCast. Note that both ShakeMap 

and ShakeCast are USGS products that are used regionally and by specific responding 

agencies, such as USNRC and FEMA. Combined, the addition of 100 new or upgraded 

stations would allow ANSS to compute earthquake source parameters more accurately for 

response and mitigation activities and would ensure a high likelihood of capturing on-scale 

ground motions within 50 km of expected moderate to large earthquakes. The additional

stations also would address regional source and propagation issues of interest to USNRC.
12

Figure 4. Map showing existing seismic stations in the central United States and planned station upgrades under American Recovery and 

Reinvestment Act (ARRA) activities (outlined in pink). Proposed augmentations are shown as blue squares (with seismic source zones) and 

purple squares (at or near nuclear powerplants).
13

Potential Strong-Motion Recording Options 

Through development of technical standards, the USGS has pursued deployment of ―Class 

A‖ and ―Class B‖ strong-motion systems for complementary uses in the regional networks. Class A 

systems are characterized by high-fidelity digitizers (nominal 19–22 bits of resolution) and lownoise accelerometers (about –140 dB self-noise at 1 Hz), while Class B systems are characterized 

by digitizers with lower nominal resolution of about 18 bits and accelerometer self-noise of about –

120 dB at 1 Hz. The difference between these two systems translates into about a factor of three in 

life-cycle cost, with Class A systems naturally costing more. Experience has taught that both 

systems have appropriate roles in long-term network monitoring within the United States, with 

Class A systems in quiet and more widely spaced deployments but Class B stations in noisy and/or 

denser deployments. Presently, NetQuakes systems (a Class B instrument manufactured by 

GeoSIG, Ltd., Switzerland) primarily are deployed in large numbers in culturally noisy, urban 

environments to improve the density of strong-motion recordings that go into urban ShakeMap 

outputs and to address issues of site response and resonance in the built-up environment. Class A 

systems primarily are deployed within RSNs in near-source regions to help with earthquake earlywarning algorithms (as in California) and routine monitoring of zones of active seismicity. Because 

of the relatively high life-cycle costs of Class A systems, fewer are being deployed, and networks 

employing a complementary mix of the two station classes are growing. Table 1 provides some 

generic features of possible strong-motion systems that could be part of upgrades to CEUS regional 

seismic networks. 

Table 1. Generic description of strong-motion system options. Class A systems typically cost about $15,000–

20,000 to purchase and install, while Class B systems typically cost about $10,000 to purchase and install. 

Operating costs range from about $2,000–5,000 per year, depending on locality and telemetry options. 
14

Justification for Enhanced Monitoring—Case Studies in Oklahoma and Illinois

Oklahoma Case Study: 2009–2010 Oklahoma Earthquake Swarm Northeast of Oklahoma City

Of about 50 measurable earthquakes each year in Oklahoma, only a few have shaking strong 

enough to be felt. In 2009, however, there were 43 felt earthquakes throughout the state, with 34 

occurring in Oklahoma County or in Lincoln County near Norman, Oklahoma. Following an M 3.8 

earthquake on January 15, 2010, the largest to date in the sequence, the USGS assisted the 

Oklahoma Geological Survey in deploying six USGS NetQuakes strong-motion systems in the 

vicinity of the felt seismicity (fig. 5).

On February 13, 2010, the six NetQuakes instruments recorded an M 3.2 earthquake (fig. 5; 

note black triangles with the OK station designation). Using arrival times picked from the 

NetQuakes records in the distance range of 2–14 km from the epicenter, the new location (fig. 5; 

note red star with SLU designation) was about 9 km different from the initial NEIC location (fig. 5; 

red star with NEIC designation). The initial NEIC location was based on arrival-time picks from all 

ANSS and TA stations within 500 km of the earthquake; the closest Transportable Array stations 

(V34A and W34A, shown on figure 5 by black triangles) are within 30–40 km from the earthquake, 

while the closest ANSS backbone stations are about 150 km from the epicenter and off the map (fig. 

5). Figure 5 does show the NEIC location (black star) from the M 3.8 earthquake of January 15,

2010, as well as the NEIC and SLU locations from the M 3.0 earthquake of February 15, 2010. (The 

M 3.8 earthquake of January 15 occurred before the NetQuakes instruments were deployed.) Both 

the M 3.8 and M 3.2 events show a systematic location bias of 8–10 km when using only the TA 

and existing ANSS stations and the AK135 velocity model.
15

Figure 5. Map summarizing relative earthquake locations for three earthquakes from the 2009–2010 

swarm near Oklahoma City, Oklahoma, determined first using only existing permanent Advanced 

National Seismic System (ANSS) and Transportable Array stations, and later including arrival-time 

information from temporarily deployed NetQuakes strong-motion recorders. Stations are denoted by 

black triangles; earthquake locations are denoted by stars. 

Modeling both the M 3.2 and M 3.0 earthquakes of February 13 and 15, 2010 

(figs. 5–6, respectively), showed the importance of on-scale, near-source observations of 

earthquakes for improved constraints on earthquake source parameters. In those cases, close stations 

mitigated the need for well-calibrated velocity models in order to produce accurate earthquake 

locations. Waveform modeling showed that modern accelerometer systems, such as the NetQuakes 

instruments, are capable of recording high-fidelity waveforms that can be used in estimations of 

earthquake moment magnitude, mechanism, and source depth. 
16

Figure 6. Regional moment tensor results for the M 3.2 February 13, 2010, Oklahoma earthquakes. The 

observed (red) and synthetic (blue) seismograms are shown for comparison for the best-fitting 

mechanism and moment magnitude. Also plotted are the best-fitting results for depths ranging from 

0.5–19 km. The location of the earthquake (yellow star) relative to the NetQuakes instruments (red 

circles) also is shown for comparison.
17

This swarm demonstrated to the USGS that systems like NetQuakes can be integrated into 

network operations rapidly and easily. By deploying such systems in areas of increased seismic 

activity, ANSS gains the ability to document earthquake source parameters much more thoroughly 

and accurately. In addition, such action would enable USGS scientists to capture a larger event of 

interest and subsequently use the improved source information to understand and model regional 

propagation and attenuation better than when events were observed only with more-distant stations. 

In the Oklahoma swarm, the USGS determined that NetQuakes instruments record relatively smallmagnitude earthquakes (M <3) quite well to distances over 20 km and can be used in waveformmodeling procedures and similarly sophisticated procedures. The National Earthquake Information 

Center (NEIC) and USGS-Menlo Park implemented procedures to acquire NetQuakes waveforms 

automatically from the field units and integrate them in NEIC and Menlo Park acquisition and 

processing systems, to ensure quick integration of the time series for standard processing (that is,

determination of event location, magnitude, and regional moment tensors) and for inclusion in 

impact-assessment products such as ShakeMap.

Illinois Case Study: February 10, 2010, M 3.8 Northern Illinois Earthquake

At 03:59 local time on Wednesday, February 10, 2010, an M 3.8 earthquake occurred about 

69 km west of Chicago (fig. 7), within 100 km of five nuclear powerplants (NPPs). The earthquake 

was strong enough to be felt by more than two million people, of whom more than 18,000 reported 

what they felt (fig. 8) through the USGS Community Internet Intensity Map web interface ("Did 

you feel it?"). The earthquake occurred in a part of the CEUS lacking dense seismic networks but 

which is in an area of interest to USNRC because of its proximity to critical facilities. Because the 

closest regional seismic station was more than 170 km from the earthquake, the initial NEIC 

location was about 9 km from the final calculated location. An improved location was possible only

through inclusion of a P-wave arrival time from an Incorporated Research Institutions for 

Seismology (IRIS) educational seismograph-program seismogram from Elgin, Illinois, at a distance 

of some 12 km from the epicenter. While it was fortunate to have a station close by, the station itself 

is uncalibrated and useful therefore only for locating the earthquake, not for modeling detailed 

source properties. In addition, no information was available about the state-of-health of the 

instrument; quality checks on its timekeeping accuracy also were unavailable. Quality-control steps 

subsequently taken for the Elgin-station waveform were based on e-mail exchanges with the science 

teacher at the hosting institution; no post-event calibration was possible. Although USGS 

seismologists were able to confirm that timing likely was accurate, that experience illustrates that 

mission-critical operations require well-developed command-and-control procedures for station 

calibration and operation, which are well established ANSS processes. While it is difficult to factor 

the occurrence of earthquakes outside expected source regions, had seismographs been installed and 

operated under ANSS protocols at or near the Illinois critical facilities, ANSS would have had 

immediate access to first-arrival time information to provide a better initial earthquake location as 

well as direct observation of waveforms and ground-shaking metrics needed for USGS ShakeMap 

and ShakeCast ("ShakeMap Broadcast") notification to the USNRC and to critical-facilities

operators (fig. 9). Such information could be very valuable if a larger event were to occur that could 

require assessment of magnitude-distance criteria used to determine plant actions. 

Lessons learned from the Illinois earthquake include the need for better regional velocity 

models to improve earthquake-location procedures in areas with only sparse regional network 

coverage, plus real-time monitoring of critical facilities across the region. Precise timing, ground-
18

shaking measurements, and waveform data at or near those northern Illinois facilities would have 

improved the accuracy of time-critical earthquake information for USNRC operations and provided 

new data of engineering interest to the USGS and USNRC mitigation programs.

Figure 7. Map showing location of the February 10, 2010, M 3.8 northern Illinois earthquake (yellow 

star). Also shown are the locations of the nuclear powerplants (NPPs, black stars) and Advanced 

National Seismic System (ANSS) seismic stations (triangles and circles) in the region.
19

Figure 8. Map showing the macroseismic intensities near Elgin, Illinois, reported from the February 2010 

earthquake based on web-based entries from the community-internet intensities project. Also shown is 

a comparison between the initial National Earthquake Information Center (NEIC) location (yellow star) 

using only Advanced National Seismic System stations and the final location (red star), which used a 

P-wave arrival time from a high-school seismograph station operating in Elgin, Ill. (approximately 9 km 

from the epicenter).
20

Figure 9. Output from ShakeCast showing estimated seismic intensities at the five closest nuclear 

powerplants (NPPs) to the February 10, 2010, M 3.8 northern Illinois earthquake, based on modeled

predictions of ground shaking. The MMI (Modified Mercalli Intensity) values for this earthquake were 

well below nominal damage thresholds (Exceedance ratios well below 1.0).
21

Future Improvements to Advanced National Seismic System and Regional Seismic Networks

It is implicit in the strategy that data from new or upgraded seismic stations in the CEUS 

initiated through coordinated USNRC and USGS efforts be available readily to all parties for 

production of routine monitoring datasets (such as earthquake catalogs), including automated 

preparation for use in USGS ShakeMap/ShakeCast response applications relevant to operation of 

critical facilities. Similarly, time series of engineering interest must be processed under a defined 

quality-assurance program and distributed for public access by the ANSS National Strong Motion 

Project. All station metadata must be fully documented and distributed through standard ANSS 

mechanisms (including anonymous ftp, station web-services, or station-client server applications), 

while all time series will be archived at an ANSS-supported waveform repository.

Future instrumentation upgrades and evaluations to be considered:

Prioritized installation of at least 38 Class A or B strong-motion systems within active CEUS 

source zones to improve characterization of earthquake parameters and collection of near-source 

ground-motion waveforms for studies of ground-motion attenuation and source scaling as well 

as for engineering applications.

Prioritized installation of at least 62 Class A or B strong-motion systems at or near critical 

(nuclear) facilities to be used for emergency-response applications, site-response studies, and 

engineering.

Coordinated deployment of aftershock monitoring systems for rapid characterization of 

earthquake sequences anywhere within the United States of importance to the USNRC mission, 

and in particular, in regions not adequately monitoring to lower magnitudes (typically less than 

M 2.5).

Expansion of the number of broadband/strong-motion aftershock systems at the USGS 

Geological Hazards Science Center from 21 to 30 to be used in studies of special interest (for 

example, aftershock monitoring) and for detailed ambient-noise and Green’s Function data 

generation for areas of interest (such as active source zones and near critical facilities).

While not discussed in detail here, both the USGS and USNRC are also interested in

application of rotational-motion sensors in structural monitoring and in the near-field rupture zone. 

The USGS has purchased several strong-motion rotation sensors in order to evaluate response 

characteristics, field worthiness, and capabilities for addressing issues related to building 

deformation and rocking following significant earthquakes. This work will proceed with significant 

coordination with USNRC research staff.

The USGS has tried to quantify the minimum level of effort required to improve 

characterization of earthquake effects at sites of interest in the near-source region. Either additional

monitoring of specific critical sites or of seismic source zones will improve the quantity, quality, 

and content of earthquake information products produced by the Advanced National Seismic 

System in support of the USNRC mission.

Development of Rapid Delivery of Parametric Ground-Motion Data

Situational awareness for potential future earthquake-induced shaking at nuclear 

powerplants and other critical facilities requires both proper instrumentation and source-parameter 

modeling and software for displaying and quantifying earthquake ground shaking relative to 

facilities of interest. ShakeCast (short for ShakeMap Broadcast) is a fully automated USGS system 
22

for delivering Advanced National Seismic System (ANSS)-generated ShakeMap products to critical 

users such as the USNRC (Lin and Wald, 2008). ShakeCast also is designed to deliver triggered 

notifications and tailored post-earthquake response products. Figure 10 provides an overview of the 

features and issues addressed by ShakeCast software.

Figure 10. Overview of the ShakeCast system for quantifying and displaying earthquake ground-shaking 

information, from the user’s perspective.
23

ShakeMap is a well-established USGS-developed tool used to portray the location 

and spatial extent of potentially damaging shaking following an earthquake (ShakeMap 

accessed at the permanent URL http://earthquake.usgs.gov/shakemap/ (accessed 04/14/2011). 

ShakeMap is generated automatically for moderate and large earthquakes nationwide. It was 

developed and primarily is used for emergency response, loss estimation, and public 

information. For an informed response to a serious earthquake, however, critical facility 

operators such as the USNRC must go beyond just looking at ShakeMap and must use it to 

predict the likely extent and severity of impacts on the facilities they regulate. ShakeCast (a 

software application for automating ShakeMap delivery, U.S. Geological Survey, available at 

the permanent URL http://earthquake.usgs.gov/research/software/shakecast/ (acce

allows regulatory agencies such as the USNRC, utilities, transportation agencies, businesses, 

and other large organizations,1to control and optimize the earthquake information they 

receive. With ShakeCast, the USNRC would automatically receive estimated shaking levels 

at nuclear plants and other critical facilities of interest, set thresholds for notification of 

damage states for each facility, and then automatically notify (by pager, cell phone, or email) 

specified persons within those organizations who are designated for response. 

In addition to real-time notification, ShakeCast can generate and deliver scenario 

earthquakes useful for developing and practicing facility response plans (fig. 11). This 

capability allows users either to evaluate risks from probable earthquakes and to develop 

procedures for emergency response or to take mitigation actions. The application includes 

routine testing of the ShakeCast system, earthquake scenario exercises, and evaluation of 

performance and response under potential earthquake conditions. ShakeCast therefore allows 

planning exercises to be performed using the same notification tools available and in place 

for responding to a real earthquake.

 

1Examples of utilities and agencies currently using ShakeCast include the Los Angeles Unified School District; 

Caltrans, California Department of Transportation; California Department of Water Resources; Division of 

Homeland Security; Utah Department of Public Safety; Federal Emergency Management Agency; U.S. 

Department of Veterans Affairs; ImageCat, Inc.; and the International Atomic Energy Agency. 

ssed 04/14/2011)
24

Figure 11. Example of ShakeCast information delivery from the M 7.8 southern San Andreas scenario earthquake used in the ShakeOut 

earthquake exercise from a prioritized list and map of Caltrans facilities displayed in the mapping mode of the ShakeCast client.

(ShakeCast/ShakeMap software uses copyrighted Google, Inc., imagery as a base for presentation of seismic information. Copyright 

remains with Google, Inc.)
25

An overview of ShakeCast capabilities and examples of user implementations can be 

found at http://earthquake.usgs.gov/research/software/shakecast/ (accessed 04/14/2011). 

Organizations typically download and install the ShakeCast software package on a hardened 

in-house computer system. The software is installed by an interactive script. Facility, 

vulnerability, and notification data are put in using import tools and simple, commaseparated (CSV) users’ files. ShakeCast comes preconfigured2

but the USGS suggests a 

custom configuration for the USNRC. The ShakeCast web interface allows an administrator 

to access all functions of their local system; the USNRC will be able to manage its own 

contact information and notification preferences.3

The USGS suggests implementing ShakeCast in two steps: (1) complete an 

assessment of real-time tools and ShakeCast implementations already at USNRC; and (2) 

perform an optimized ShakeCast system implementation. The assessment step would consist 

of (a) determining the appropriate ANSS real-time products (ENS, CISN-Display, ShakeCast 

Prototype) for USNRC users with different responsibilities or at different locations; 

(b) holding a stakeholder workshop at either/both USGS and USNRC; and (c) developing a 

project plan (―white paper‖) and a timeline for accomplishing the plan. In the workshops, the 

following topics could be reviewed: case histories in the use of ShakeCast (Caltrans, 

Department of Water Resources, etc.); IT security and related IT issues; the potential for 

collection and use of site-specific ground-motion data; and project goals and timeline. 

To implement the ShakeCast System at the USNRC, USGS would work with 

USNRC staff as so-called ―critical users‖ to custom-harden ShakeCast and redesign the 

software subsystem as necessary for the USNRC application and to address ShakeCast RSS 

delivery speed and robustness. The USNRC would be provided with specific documentation 

for its critical operational environment. The USNRC would provide a list of facilities and 

vulnerabilities for ShakeCast configuration and develop its preferences for notifications and 

alert criteria. Over the longer term, the USGS would provide customer service support, 

ongoing training, IT interaction, and a support helpline. 

Further research and development is needed to customize ShakeCast for USNRCspecific interests, including provision of ShakeMap operational support for the CEUS 

systems-backbone station parametric data from the ANSS regional nets; triggering; and 

inclusion of macroseismic data. A customized suite of ground-motion prediction equations is 

needed for CEUS ShakeMaps. In addition, the ShakeMap atlas needs to be expanded to 

include all historic events of USNRC interest, and USNRC-selected scenarios should be 

developed in ShakeCast as system tests and scenarios.

 

2

Information Technology (IT) security is a primary concern for users requiring automatic electronic delivery of 

information. By taking advantage of standard Internet protocols, ShakeCast users avoid most typical corporate 

and government concerns and firewall limitations. By using Really Simple Syndication (RSS) and interval 

polling, users initiate all communications with the USGS web servers that host ShakeMap and retrieve selected 

products as a request rather than a ―push.‖ This RSS approach allows users to update software automatically 

under conditions of their own choosing. 

3

ShakeCast software is built upon open-source tools, providing standard, freely available software for all users, 

encouraging user improvements, and simplifying interfacing with existing users’ response tools. ShakeCast uses 

the Apache Web server and PHP (Hypertext Preprocessor) for dynamic web content, MySQL for facility and 

notification databases, and is wrapped in Practical Extraction and Report Language (PERL) scripting. Exchange 

files are in Extensible Markup Language (XML) for standardized interfacing with web, geographic information 

system (GIS), spreadsheet, database, and other applications. 
26

Summary

Characterization of potential earthquake ground motions through enhanced seismic 

monitoring capabilities demonstrates important elements for the evaluation of seismic 

hazards at critical facilities. This report to the U.S. Nuclear Regulatory Commission—a 

Phase 2 report— focuses on evaluation and improvement of seismic monitoring capabilities 

in the central and eastern United States in support of future public safety and regulatory 

needs, particularly with respect to known seismic zones (such as the East Tennessee Seismic 

Zone, the New Madrid Fault Zone, the Charleston Seismic Zone, and others) and proximity 

to nuclear powerplant sites. The evaluation of monitoring capabilities is strengthened by the 

National Science Foundation Transportable Array, a large set of monitoring stations 

traversing the country in appraisal of seismicity, crustal structure, and active source zones. 

The American Recovery and Reinvestment Act has also provided a unique opportunity to 

improve monitoring capabilities through upgrades to networks of the USGS Advanced 

National Seismic System (ANSS) of monitoring stations. Conceptually, the USGS and other 

partners such as the USNRC can leverage their respective seismic hazards and mitigation 

activities by using ANSS as an effective national seismic-data collection, processing and 

distribution platform.

Within the central and eastern United States, the USGS suggests that improved 

seismic monitoring should include deployment of at least 38 new ANSS strong-motion 

stations in seismically active central and eastern United States earthquake source zones to 

improve seismic monitoring to address issues in the source region, as well as 62 new strongmotion stations specifically located near critical facilities such as nuclear powerplants to 

address issues of seismic wave propagation and site response in the vicinity of those sites. 

Key transportable-array stations should also be evaluated as potential permanent stations as 

part of ANSS regional seismic networks. Related objectives include expansion of seismic 

databases for ground-motion data to lower-magnitude events needed to address earthquake 

source characterization, attenuation, and propagation across the central and eastern United 

States, including implementation of improved USGS ShakeMap and ShakeCast tools for 

enhanced communication of earthquake intensity and characteristics to the USNRC and other 

critical facility operators to support rapid response and assessment activities. Network 

improvements also are considered through a mix of strong-motion systems, using moreexpensive high-resolution instruments in a complementary mix that includes lowerresolution, lower-cost units in culturally noisy urban environments to improve the density of 

strong-motion recordings in built-up areas; the higher-cost instruments can be placed for best 

monitoring of active seismic areas. Two case studies of actual earthquakes in Oklahoma and 

near Chicago attest to the value of the various data arrays and data-evaluation methods. 

These and other approaches further leverage the ARRA upgrades through governmental, 

university, national laboratory, and Canadian efforts. Because the USGS and regional 

partners operate monitoring networks under broad instrumentation, metadata, and dataexchange protocols, addition of new stations in the central and eastern United States is costeffective and relatively easy. Targeted upgrades to monitoring networks will provide data to 

reduce uncertainty in hazard estimation of low-probability events and improve confidence in 

seismic design. The strong-motion monitoring is an essential part of this long-term strategy. 

These considerations of monitoring and data-handling support for enhancement of 

instrument upgrades (a mix of strong-motion stations) focused on seismically active zones 

and specifically on critical infrastructure such as nuclear powerplant sites. Such approaches 
27

improve characterization of earthquake parameters and collection of near-source groundmotion waveforms for studies of attenuation, scaling, and engineering applications. Improved 

capabilities and characterization of aftershock sequences and expansion of ground motion 

datasets is addressed by consideration of approaches to monitor adequately to lower 

magnitude(s) through rapid deployment of additional broadband and strong-motion 

monitoring systems housed at the USGS Geologic Hazards Science Center, and targeted 

studies of ambient noise in active source zones near critical facilities.

Finally, the report considers the near real-time situational awareness offered by 

proper instrumentation and source-parameter modeling, along with delivery of such 

analytical information to users in the nuclear powerplant community through use of USGS 

products such as ShakeCast. That automated system can provide rapid information to critical 

users such as the USNRC, covering details of an event and estimated damage assessment, 

along with updates based on aftershock events. The same system can be configured for use in 

realistic training scenarios for exercises in emergency planning and response.

Acknowledgments

Numerous collaborators provided input, ideas, or elements of text for this report. 

Because of the primary effort by the listed authors and the wide disparity of contributions as 

to size or significance, we have determined that the best way to acknowledge those 

contributions is by listing collaborators and affiliations as follow here. We are grateful for all 

contributions to our understanding of the task of enhancing and strengthening observations of 

seismic events with respect to safety at critical facilities such as nuclear powerplants. We 

also gratefully acknowledge assistance from the U.S. Nuclear Regulatory Commission 

through Interagency Joint Agreement JCN-N6184.
28

Contributors

 Leith, William ANSS Coordinator 

 Principal Investigator U.S. Geological Survey 

Reston, VA 20192 

 Benz, Harley ANSS Technical Manager 

 Co-principal Investigator U.S. Geological Survey 

Denver, CO 80225 

 Herrmann, Robert Professor of Earth Sciences 

 Principal Consultant St. Louis University 

St. Louis, MO 63103 

 Ebel, John Professor of Earth Science

Boston College 

Boston, MA 02467 

 Evans, John Research Geophysicist

U.S. Geological Survey 

Menlo Park, CA 94025 

 Fletcher, Joe Research Geophysicist

U.S. Geological Survey 

Menlo Park, CA 94025 

 Frankel, Arthur Research Geophysicist

U.S. Geological Survey 

Seattle, WA 98195

 Kim, Won-Young Research Geophysicist

Lamont-Doherty Earth Observatory of 

Columbia University 

Palisades, NY 10964 

 McNamara, Daniel Research Geophysicist

U.S. Geological Survey 

Denver, CO 80225 

 Nigbor, Robert Research Civil Engineer

University of California at Los Angeles 

Westwood, CA 90024 

 Owens, Thomas Professor of Earth Science

University of South Carolina 

Columbia, SC 29208 

 Wald, David Research Geophysicist

U.S. Geological Survey

Denver, CO 80225

 Withers, Mitch Research Geophysicist

Center for Earthquake Research and 

Information of the University of Memphis 

Memphis, TN 38152 

 Woodward, Robert Incorporated Research Institutions for Seismology 

 Washington, D.C. 20005 
29

Selected References

Lin, K.-W., and Wald, D.J., 2008, SHAKECAST users manual: U.S. Geological Survey OpenFile Report 2008-1158, 90 p.

U.S. Nuclear Regulatory Commission, 2008, Nuclear Regulatory Commission Seismic 

Research Program Plan, Fiscal Years 2008–2011: U.S. Nuclear Regulatory Commission, 

January 2008, 48 p.

U. S. Geological Survey, 1999, An assessment of seismic monitoring in the United States—

Requirement for an Advanced National Seismic System: U.S. Geological Survey Circular

1188, 55 p.

U. S. Geological Survey, 2009, ANSS—Advanced National Seismic System: U.S. 

Geological Survey, unpaginated, accessed 04/14/2011, at 

http://earthquake.usgs.gov/research/monitoring/anss (for published performance 

standards).

Publishing support provided by: 

Denver Publishing Service Center

For more information concerning this publication, contact:

Center Director, USGS Geologic Hazards Science Center 

Box 25046, Mail Stop 966

Denver, CO 80225

(303) 273-8579

Or visit Geologic Hazards Science Center Web site at:

http://geohazards.cr.usgs.gov/
Leith and others—Earthquake Monitoring in the United States: Support of Seismic Assessments for Critical Facilities—Open-File Report 2011–1101