U.S. Department of the Interior 

U.S. Geological Survey 

Feasibility Study of Earthquake Early 

Warning (EEW) in Hawaii 

Open-File Report 2016–1172
COVER: Earthquake early warning systems, like ShakeAlert, work because the warning 

message can be transmitted almost instantaneously, while shaking waves from the 

earthquake travel through the Earth at speeds of a few miles per second. When an earthquake 

occurs, seismic waves—including compressional (P) waves, transverse (S) waves, and 

surface waves—radiate outward from the epicenter. The faster but weaker P waves trip 

nearby sensors, causing alert signals to be sent out, giving people and automated electronic 

systems some time (seconds to minutes) to take protective actions before the arrival of the 

slower but stronger S waves and surface waves. Computers and mobile phones receiving the 

alert message can calculate the expected arrival time and intensity of shaking at your location.

(From Burkett and others, 2014)
Feasibility Study of Earthquake Early Warning 

(EEW) in Hawaii 

By Weston A. Thelen, Alicia J. Hotovec-Ellis, and Paul Bodin 

Open-File Report 2016–1172

U.S. Department of the Interior 

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

SALLY JEWELL, Secretary 

U.S. Geological Survey 

Suzette M. Kimball, Director 

U.S. Geological Survey, Reston, Virginia: 2016 

For more information on the USGS—the Federal source for science about the Earth, 

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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: 

Thelen, W.A., Hotovec-Ellis, A.J., Bodin, P., 2016, Feasibility study of earthquake early 

warning (EEW) in Hawaii: U.S. Geological Survey Open-File Report 2016–1172, 30 p., 

http://dx.doi.org/10.3133/ofr20161172. 

ISSN 2331-1258 (online)
iii

Contents

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

Introduction....................................................................................................2

Current State of the Seismic Network..................................................................7

Theoretical Performance of ElarmS and a Single Station Within the Current Network...12

Testing of ElarmS Within the Current Network...................................................19

Steps Toward Full EEW Implementation.............................................................19

ElarmS Compared to a Single-Station Approach...................................................27

Summary.....................................................................................................28

References Cited...........................................................................................29

Figures

1. Schematic cross-section of the common sources of damaging earthquakes in the 

State of Hawaii ..............................................................................................................3

2. Map of M≥6 earthquakes in the State of Hawaii since 1868 .........................................4

3. Seismic hazard map of the State of Hawaii ..................................................................5

4. Schematic diagram of an earthquake early warning system.........................................6

5. Current seismic station map within the State of Hawaii ................................................9

6. Station density plot (distance to nearest four stations) within the State of Hawaii ......10

7. Histograms of latency and packet size of existing stations as measured on the 

earthquake early warning processing server...............................................................12

8. Warning time to Hilo, Kailua-Kona and the summit of Mauna Kea from different source 

areas considering the existing earthquake early warning stations and latency ...........14

9. Warning times to Honolulu from different source areas considering the existing 

earthquake early warning stations and data latency....................................................18

10. Map of proposed station upgrades and contour map of station density (distance to 

the nearest four stations).............................................................................................21

11. Warning time to Hilo, Kailua-Kona, and the summit of Mauna Kea from different 

source areas, assuming incorporation of all the proposed upgrades to stations and 

telemetry .....................................................................................................................23

12. Warning time to Honolulu from different source areas, assuming incorporation of all 

the proposed upgrades to stations and telemetry .......................................................26

Tables

1. List of instrument sites that could be upgraded to contribute to an earthquake early 

warning network, listed by descending upgrade score................................................22

2. Current and idealized theoretical ElarmS warning times to areas of high population or 

critical infrastructure on the Island of Hawaiʻi for notable historical earthquakes.........27

3. Theoretical warning times to areas of high population or critical infrastructure on the 

Island of Hawaiʻi, comparing an idealized ElarmS system and a single-station approach 

for some damaging earthquakes of note .....................................................................28
1

Feasibility Study of Earthquake Early Warning 

(EEW) in Hawaii

By Weston A. Thelen1, Alicia J. Hotovec-Ellis2, and Paul Bodin2

Executive Summary

The effects of earthquake shaking on the population and infrastructure across the State of Hawaii

could be catastrophic, and the high seismic hazard in the region emphasizes the likelihood of such an 

event. Earthquake early warning (EEW) has the potential to give several seconds of warning before 

strong shaking starts, and thus reduce loss of life and damage to property. The two approaches to EEW

are (1) a network approach (such as ShakeAlert or ElarmS) where the regional seismic network is used 

to detect the earthquake and distribute the alarm and (2) a local approach where a critical facility has a 

single seismometer (or small array) and a warning system on the premises. 

The network approach, also referred to here as ShakeAlert or ElarmS, uses the closest stations 

within a regional seismic network to detect and characterize an earthquake. Most parameters used for a

network approach require observations on multiple stations (typically 3 or 4), which slows down the 

alarm time slightly, but the alarms are generally more reliable than with single-station EEW approaches.

The network approach also benefits from having stations closer to the source of any potentially 

damaging earthquake, so that alarms can be sent ahead to anyone who subscribes to receive the 

notification. Thus, a fully implemented ShakeAlert system can provide seconds of warning for both 

critical facilities and general populations ahead of damaging earthquake shaking. For example, using a 

fully implemented ShakeAlert system, a repeat of the shallow M7.9 1868 Ka‘ū earthquake could send 

alarms with 12 to 14 seconds of warning for the communities of Hilo and Kailua-Kona, as well as for 

the Mauna Kea telescopes. The city of Honolulu would receive a full 70 seconds of warning before 

shaking began. If there were a repeat of the deeper M6.7 2006 Kīholo Bay earthquake, ShakeAlert could 

send alarms with 15, 3, and 6 seconds of warning for Hilo, Kailua-Kona, and the Mauna Kea telescopes, 

respectively, and Honolulu would receive an alarm 47 seconds ahead of shaking.

The cost to implement and maintain a fully operational ShakeAlert system is high compared to a 

local approach or single-station solution, but the benefits of a ShakeAlert system would be felt 

statewide—the warning times for strong shaking are potentially longer for most sources at most 

locations.

The local approach, referred to herein as “single station,” uses measurements from a single 

seismometer to assess whether strong earthquake shaking can be expected. Because of the reliance on a 

single station, false alarms are more common than when using a regional network of seismometers.

Given the current network, a single-station approach provides more warning for damaging earthquakes 

that occur close to the station, but it would have limited benefit compared to a fully implemented 

ShakeAlert system. For Honolulu, for example, the single-station approach provides an advantage over 

ShakeAlert only for earthquakes that occur in a narrow zone extending northeast and southwest of 

O‘ahu. Instrumentation and alarms associated with the single-station approach are typically maintained 

 

1U.S. Geological Survey. 

2University of Washington. 
2

and assessed within the target facility, and thus no outside connectivity is required. A single-station 

approach, then, is unlikely to help broader populations beyond the individuals at the target facility, but 

they have the benefit of being commercially available for relatively little cost.

The USGS Hawaiian Volcano Observatory (HVO) is the Advanced National Seismic System 

(ANSS) regional seismic network responsible for locating and characterizing earthquakes across the 

State of Hawaii. During 2014 and 2015, HVO tested a network-based EEW algorithm within the current 

seismic network in order to assess the suitability for building a full EEW system. Using the current 

seismic instrumentation and processing setup at HVO, it is possible for a network approach to release an 

alarm a little more than 3 seconds after the earthquake is recorded on the fourth seismometer. Presently, 

earthquakes having M≥3 detected with the ElarmS algorithm have an average location error of 

approximately 4.5 km and an average magnitude error of -0.3 compared to the reviewed catalog 

locations from the HVO. Additional stations and upgrades to existing seismic stations would serve to 

improve solution precision and warning times and additional staffing would be required to provide 

support for a robust, network-based EEW system.

For a critical facility on the Island of Hawaiʻi, such as the telescopes atop Mauna Kea, one 

phased approach to mitigate losses could be to immediately install a single station system to establish 

some level of warning. Subsequently, supporting the implementation of a full network-based EEW

system on the Island of Hawaiʻi would provide additional benefit in the form of improved warning 

times once the system is fully installed and operational, which may take several years.

Distributed populations across the Hawaiian Islands, including those outside the major cities and 

far from the likely earthquake source areas, would likely only benefit from a network approach such as 

ShakeAlert to provide warnings of strong shaking.

Introduction

Earthquakes are a well known phenomenon in the State of Hawaii, especially among residents of 

the Island of Hawaiʻi, who may feel tens of earthquakes each year. While some felt earthquakes occur 

directly in association with volcanic processes, most of the largest (M≥6) earthquakes occur within two 

source zones (figs. 1 and 2; Klein and others, 2001). Indirectly, many of the earthquakes are related to 

the presence and mass of the volcanic islands and magmatic activity at young volcanoes.

The first source zone for large earthquakes (M≥6) is at the nearly flat boundary between the 

erupted basalt of the volcanic islands and the old ocean floor upon which the islands are built (Crosson 

and Endo, 1982, Got and others, 1994). Called a “décollement,” this interface is about 6 mi (~10 km)

beneath the coastline and was the source of the M7.0 and M7.9 earthquakes in Kaʻū in 1868 and the 

M7.2 and M6.2 earthquakes near Kalapana in 1975 and 1989, respectively (fig. 2; Swanson and others, 

1976; Lipman and others, 1985; Wyss, 1988). Though a décollement is present under all of the 

Hawaiian Islands, damaging earthquakes are most likely to occur on the south and west sides of the 

Island of Hawaiʻi, where active rift zones are present (Klein and others, 2001).

The second main source of large earthquakes occurs deep beneath the island and ocean crust in 

the mantle below. Earthquakes in this zone generally occur 13 mi (21 km) or deeper and are thought to 

be a result of the stresses in the mantle arising from the weight of the volcanic islands above (for 

example, Wolfe and others, 2004). The most recent examples of this type of earthquake are the Kīholo

Bay earthquake (M6.7) and Māhukona earthquake (M6.1), which both occurred in 2006 and caused

significant damage on the Island of Hawaiʻi and disruptions on O‘ahu (fig. 2, Yamada and others, 

2010). Large mantle earthquakes since 1868 are more widespread than décollement earthquakes and

may have occurred as far north as Moloka‘i: it is believed that the M6.8 earthquake near Lāna‘i in 1871 

and the M6.9 earthquake north of Maui in 1938 may have been mantle earthquakes (fig. 2; Wyss and 

Koyanagi, 1992; Klein and others, 2001).
3

Figure 1. Schematic cross-section of the common sources of damaging earthquakes in the 

State of Hawaii. The décollement source (upper yellow star) occurs between the volcanic 

island (brown) and the underlying ocean crust (gray) along the ancient ocean floor (thin red 

line). Arrows indicate the direction of movement of the island over the ocean crust during 

décollement earthquakes. Décollement earthquakes are most common along the south and 

west coasts of the Island of Hawaiʻi. The mantle source (lower yellow star) occurs within the 

mantle (black). Mantle earthquakes can occur anywhere within the Hawaiian Islands, but are 

most common under the Island of Hawaiʻi. Other smaller earthquakes may occur on lesser 

crustal earthquakes (thin black lines) or along volcanic conduits (black vertical pipe and 

orange circular magma chamber).

Since 1868 there have been at least 51 earthquakes M≥6 across the State of Hawaii, with the 

overwhelming majority of the damaging earthquakes occurring near the Island of Hawaiʻi, where the 

volcanism is most active and the loads from overlying islands highest (Klein and others, 2001; Wyss 

and Koyanagi, 1992; fig. 2). The U.S. Geologic Survey (USGS) has calculated the seismic hazard for 

the whole State (fig. 3), and the results show that the areas of highest hazard are on the south part of the 

Island of Hawaiʻi, with decreasing hazard northwestward. On the south part of the Island of Hawaiʻi, the 

seismic hazard is similar to living on or in close proximity to the San Andreas Fault in California (Klein 

and others, 2001). Despite having a significantly lower hazard than the south part of the Island of 

Hawaiʻi, O‘ahu has a seismic hazard similar to many parts of the Intermountain West.
4

Figure 2. Map of M≥6 earthquakes in the State of Hawaii since 1868 (modified from Klein and 

others, 2001). A, Earthquakes, shown by red dots and open circles sized according to 

magnitude, annotated with the year of occurrence and magnitude. Black box shows extent of 

map in B. Large earthquakes are only denoted if they occur outside the box. B, Earthquakes 

on the Island of Hawaiʻi, shown by red dots and sized according to magnitude, with year and 

magnitude denoted for each earthquake. Earthquake sizes in A and B are not scaled 

equivalently. Annotations with stars afterward refer to earthquakes in tables 2 and 3.
5

Figure 3. Seismic hazard map of the State of Hawaii. The percentage of the acceleration of 

gravity (percent g) is plotted that has a 2 percent chance of exceedance within 50 years at a 

seismic wave period of 0.3 s (3 Hz). Warm colors indicate a higher percent g, which can be 

used as a proxy for higher seismic hazard. Modified from Klein and others (2001). 

The USGS Hawaiian Volcano Observatory (HVO) has been monitoring earthquakes since the 

inception of the observatory in 1912. A modern seismic network has been cataloging the occurrences of 

earthquakes since 1959. HVO has continuously incorporated new technologies and techniques to 

improve earthquake monitoring both for large and damaging earthquakes and for smaller earthquakes 

that assist in assessing volcanic hazard. The USGS Advanced National Seismic System (ANSS) 

recognizes HVO as the authoritative regional seismic network for the State of Hawaii and thus, HVO 

has the responsibility of calculating and reporting earthquake locations, magnitudes, and earthquake 

products to emergency managers and the public for preparedness and situational awareness. HVO also 

serves as the authoritative organization for assessing volcanic hazards in the State of Hawaii and issuing 

public notifications of volcanic activity.

Advances in instrumentation density, detection and calculation techniques, and data transmission 

technology now make it possible to detect a large earthquake and send notice prior to the onset of strong 

shaking. Called Earthquake Early Warning (EEW), the concept is to locate and characterize an 

earthquake using the instruments closest to the earthquake and to calculate the intensity of ground 

shaking, then send warning to affected groups and individuals at risk (fig. 4). EEW systems have 

already been established in the countries of Japan and Mexico. An EEW system on the West Coast of 

the United States is being developed, called ShakeAlert (Given and others, 2014); in this study, we 

assess the feasibility of portions of the ShakeAlert system for the State of Hawaii.
6

Figure 4. Schematic diagram of an earthquake early warning system. From Given and others

(2014).

Despite having a very high seismic hazard (high likelihood of strong shaking), the seismic risk

(exposure of population and infrastructure to the hazard) in the State of Hawaii is low compared to the 

West Coast of the United States, which has large population and complex infrastructure across a wide 

geographic area. However, there are critical structures and populations that would significantly benefit 

from the development of an EEW system in the State of Hawaii. The largest towns on the Island of 

Hawaiʻi include Hilo (population 43,263; United States Census Bureau, 2010) and Kailua-Kona 

(population 11,975; United States Census Bureau, 2010). Despite modest permanent populations, daily 

average visitors to Hilo and Kailua-Kona are 6,025 and 23,983, respectively (Hawaiʻi Tourism 

Authority, 2016). In addition, the State capital, Honolulu, has 337,256 people as of 2010 and nearly 1

million people reside on the Island of Oʻahu (United States Census Bureau, 2010). An additional daily 

average of 96,013 visitors on Oʻahu adds to that total (Hawaiʻi Tourism Authority, 2014). In terms of 

infrastructure, the telescopes on Mauna Kea and Haleakalā could benefit significantly by taking 

advantage of warning times of strong shaking from an EEW system to mitigate damage—some of them

were damaged during the M6.7 Kīholo Bay earthquake in 2006. If given a short-term warning of strong 

shaking, elevators could be stopped, firehouse doors could be raised and delicate medical procedures 

stopped. Individuals with advance warning could drop, cover and hold on prior to the shaking or pull 

their cars over to the side of the road.

Earthquakes generate a variety of types of waves, however, for our purposes, we are only 

concerned with the fastest waves near the surface (primary waves or p-waves) and the slower waves that

produce the strongest shaking (secondary waves or s-waves and surface waves). In EEW systems, the pwave is typically analyzed to calculate both the location and magnitude of the earthquake; from those 

results, the intensity of shaking is estimated for the entire region. By using the first part of the p-wave 

recording on just a few of the stations closest to the earthquake, an EEW system can send a warning of 
7

ground shaking ahead of when the s-wave (and strong shaking) actually arrives at particular location.

The amount of warning depends on several factors, but generally the farther away from the earthquake, 

the more warning an individual or structure would have. At the epicenter, or location, of the earthquake 

there may be a “blind zone” where no warning can be given because not enough observations have been 

gathered or the processing time is too great to send a warning before the shaking starts. The size of the 

blind zone can change depending on the depth of the earthquake, the density of stations around the 

earthquake, and the processing time needed to produce and transmit the alarm. The area of the blind 

zone can be reduced with denser station coverage and with faster transmit and processing times, but 

may never be zero—extremely shallow earthquakes that occur close to a population or facility of 

concern will experience shaking from shear waves before the alarm reaches them.

There are several approaches to EEW, which can be distilled into two categories: a single-station 

approach and a network approach. The single-station approach uses a single seismometer or small array 

of sensors at the same location, and thus can produce a very fast warning for earthquakes that occur 

close to the sensor; however, the quality of that warning may be lower as it is susceptible to noise on 

any given station (Böse and others, 2009). Typically, the single-station approach is favored for critical 

facilities because of its relatively low cost; alarms generated within a single-station system are generally 

used only to mitigate damage to that facility or immediate area.

The network approach uses a distributed array of seismometers, typically a regional seismic 

network, to detect and characterize a large earthquake. One network approach, called ElarmS, can 

trigger an alarm within less than 1 second of detecting a p-wave at a station and then continues to 

evaluate the first 4 seconds of the earthquake (Kuyuk and others, 2014). ElarmS is one of three 

algorithms embedded within the ShakeAlert software that is being implemented in the EEW-system on 

the West Coast of the United States. To reduce false alarms, triggers at four stations are required to 

determine the location and magnitude and to issue an alert (Kuyuk and others, 2014). As more 

observations of the earthquake are available, those observations are used to refine the solution and thus

improve the estimate of shaking. Because algorithms using a network approach, like ElarmS, require 

multiple observations, the alarms produced may be slower than a single station algorithm for 

earthquakes very close to a critical facility or impacted population, but still faster than a single station 

algorithm for earthquakes farther away. Alarms are also more reliable as the algorithms using a network 

approach depend on several stations instead of one (Allen and others, 2009). In areas of high station 

density (10 km spacing) in California, ElarmS and ShakeAlert have issued warnings 4 seconds after an 

earthquake begins (Burkett and others, 2014). The network approach to EEW is more costly to 

implement, but has more potential benefit, as any public or private entity can sign up for shaking alerts 

and either design measures to reduce damage to infrastructure or educate themselves on what to do in 

the case of a shaking alarm (for example, Drop, Cover and Hold On!). 

This paper details the feasibility of an EEW system in the State of Hawaii. First we discuss the 

current seismic network and the performance of the ElarmS algorithm of the ShakeAlert system within 

the current network. We explore the potential benefits and pitfalls of a single-station versus a network 

approach (such as ShakeAlert). Finally, we discuss what would be needed for a full implementation of 

the ShakeAlert system in Hawaii.

Current State of the Seismic Network

The current inventory of seismometers in the State of Hawaii is split between several operators, 

each with different priorities and goals for their instruments (fig. 5). Most EEW systems only use 

continuous broadband seismometers (sensitivity < 10 s period) and continuous strong motion 

accelerographs, and thus, only a subset of HVO’s stations can be used (many stations are short-period 

seismometers). It is common practice, when resources exist, to install both a continuous broadband 
8

seismometer and a continuous strong motion accelerograph at the same site so as to be able to measure a 

range of amplitudes and frequencies (for example, low-amplitude long period waves, and s-waves from 

strong local earthquakes) with high fidelity. As of 2016, HVO operates 24 continuous broadband 

stations and 19 continuous strong motion accelerographs, nearly all on the Island of Hawaiʻi and densest 

around the summit and rift zones of Kīlauea and Mauna Loa (fig. 5). The placement of seismometers 

reflects the desire of the HVO to track small earthquakes associated with volcanic processes, though 

there are stations distributed across the Island of Hawaiʻi to track non-volcanic seismicity. The NOAA 

Pacific Tsunami Warning Center (PTWC) operates 19 real-time continuous stations that are distributed 

across the Hawaiian Islands in order to better characterize the tsunami hazard that arises from large 

Hawaiian earthquakes and to notify officials. All PTWC stations have strong-motion accelerographs, 

though only a subset have co-located broadband seismometers. The Global Seismograph Network 

(GSN) operates a real-time continuous station on the Island of Hawaiʻi and a real-time continuous 

station on the Island of O‘ahu, both of which bolster the ability of the GSN to track global seismicity.

As of 2016, the only continuous data channels are from broadband seismometers, though triggered 

strong-motion accelerometers do exist at each site. Lastly, the National Strong Motion Program (NSMP) 

operates approximately 30 strong-motion accelerographs capable of recording very large ground 

motions. The stations are well distributed, however they are typically in buildings or structures that

make the records noisy unless the ground motion is very large. Furthermore, the NSMP stations only 

produce data tens of seconds to a few minutes after a strong earthquake occurs and cannot, as of 2016, 

contribute to an EEW system. The number of unique sites available for EEW as of 2016, which either 

have a continuous broadband seismometer, a continuous strong motion accelerograph, or both is 56 

across the State of Hawaii.

For the purposes of earthquake early warning, the closer an earthquake occurs to a single station 

(assuming a single station algorithm) or a set of stations (assuming a network approach like

ElarmS/ShakeAlert), the faster an estimate of shaking can be produced and an alert sent to an end user.

Therefore, earthquakes that occur in areas of higher station density will generally produce a faster alarm 

and have a relatively small or no blind zone. Considering the entirety of stations available for an EEW 

system in the State of Hawaii, the station density is highest around Kīlauea summit and East Rift Zone 

and the summit of Mauna Loa (fig. 6). Away from these areas, station density falls dramatically, 

especially to the north and northwest. Thus, given the current station configuration, earthquakes that 

occur on the south part of the Island of Hawaiʻi will generally have faster alert times than earthquakes 

that occur on other parts of the Island of Hawaiʻi. Within the 250 miles between Maui and Kaua‘i, there 

are only 10 continuous stations; 5 of those are on O‘ahu and there are none on Lāna‘i. Practically, this 

means that people within the vicinity of a large earthquake near Maui, Lāna‘i, or Moloka‘i are unlikely 

to benefit from an EEW system without additional instrumentation, although they could benefit from 

alerts for large events on the Island of Hawaiʻi.
9

Figure 5. Current seismic station map within the State of Hawaii. Triangles are stations that 

could contribute to an earthquake early warning (EEW) system; colors indicate which agency 

operates the station. Black dots are existing stations that are not useful for earthquake early 

warning, either because of the instrumentation or type of recording. These stations could be 

upgraded to make them useful for earthquake early warning. A, Map of stations throughout the 

Hawaiian Islands. B, Stations on the Island of Hawaiʻi. 
10

Figure 6. Station density plot (distance to nearest four stations) within the State of Hawaii.

Black triangles are stations that could be used in an earthquake early warning (EEW) system.

Contour lines represent the distance, in kilometers, to the nearest four stations. A, Station 

density across the State of Hawaii. B, Station density across the Island of Hawaiʻi.
11

The reliability of an EEW system is dependent on the robustness of the facilities that receive the 

data and the links from those facilities to the remote instruments in the ground (telemetry). Currently, all 

seismic data for use in EEW is received at HVO. Located within Hawaiʻi Volcanoes National Park on 

the rim of Kīlauea Volcano, the HVO can be vulnerable to connection problems to the Internet because 

of weak communications infrastructure on the Island of Hawaiʻi. Without a reliable connection to the 

Internet, it is unlikely that EEW notifications could be released. To address this problem, HVO has 

recently completed a microwave link directly from HVO to the Daniel K. Inouye Regional Center on 

Ford Island, which lies within Pearl Harbor on the Island of O‘ahu. The link uses the ʻĀnuenue

network, which is operated by the United States Coast Guard and relied upon for robust 

communications through a variety of natural disasters. HVO is in the process of building an offsite

backup facility for the seismic network at Ford Island in a space that is shared by PTWC servers. Once 

completed, the presence of an offsite backup will allow seismic operations to be much more resilient in 

the wake of telecommunications failures and natural disasters on the Island of Hawaiʻi that affect the 

local operation of HVO. As part of any EEW buildout in Hawaii, a backup server would be co-located 

with the offsite facility on Ford Island and would benefit from the redundancy that comes with a full 

offsite backup facility. Current telemetry for stations used in EEW is naturally diverse because of the 

different agencies that operate the stations and their various approaches to data transmission. HVO’s

EEW-ready stations currently all use an internal telemetry network, which has demonstrated reliability 

during hurricanes and tropical storms. However, this internal telemetry network is maintained by HVO, 

which is not currently staffed during nights and weekends. PTWC stations transmit most of their data

over cell modems, which can be susceptible to Internet outages, but their network has also successfully

withstood hurricanes and tropical storms. Further, the PTWC facility on Ford Island is staffed 24 hours 

a day and has robust power and communications infrastructure.

The effectiveness of an EEW system relies on very rapid messaging, which, in turn, depends 

both on the time it takes to receive the data from the remote station and the time to process that data.

Different agencies collect and transmit their data differently, and so some considerations arise for a 

network approach that uses data from HVO, PTWC, and GSN, as EEW in Hawaii would. The 

difference in time between when the earthquake occurs and when the data arrives at the datacenter is 

called station latency. Lower latencies allow for faster EEW notifications for end users. The station 

latency can be further divided into the time it takes for the digitizer at the station to collect and assemble 

the data from the seismometer (the length of the time packet), and the time it takes to transmit the data.

In 2009, HVO upgraded all of their stations to use the Reftek RT130 digitizer, which waits for a buffer 

to fill up to a certain size before sending it to the datacenter. This results in a packet size of about 5 

seconds for broadband stations and 9 seconds for strong motion accelerographs (fig. 7). The latency 

associated with the telemetry is between 1.8 and 3.8 seconds, depending on the strength of the link (fig. 

7). All HVO stations that would be used in an EEW system traverse the observatory’s own telemetry 

network. Stations operated by PTWC use a different kind of digitizer, which sends packets every 

second, reducing the latency but increasing the bandwidth requirements of the telemetry. Telemetry of 

stations operated by PTWC is largely over cell modem and has to be exported to HVO for EEW 

processing, producing latencies of 2.2 to 4 seconds (fig. 7). Some of the latency in HVO data is due to 

the large packet sizes, which must be fully transmitted before proceeding. There are two instances of 

PTWC stations with 1-second packet length transmitting data over HVO’s telemetry network. In both 

cases, the 1-second packets have telemetry latencies around 0.95 seconds. The situation of digitizers 

producing 1-second packets and with telemetry latencies of 0.95 seconds represents the minimum 

latency that we may expect from all stations if the current seismic network was optimized for an EEW 

system. The two stations contributed by the GSN have packet lengths of 10 to 12 seconds and telemetry 

latencies of around 5 seconds, mostly because of the large packet sizes.
12

Figure 7. Histograms of latency and packet size of existing stations as measured on the 

earthquake early warning processing server. A, Histogram of telemetry latency in seconds.

Most stations have telemetry latency between 2 and 3 seconds. Under optimal circumstances, 

telemetry latency could be reduced to less than 1 second. B, Histogram of packet size. Some 

digitizers have packets with a length of 1 second (Kinemetrics Q330 and Basalt digitizers);

however, most stations have packet sizes that are larger (RefTek RT130 digitizers). Packet 

sizes of 1 second are the shortest packet that we can expect for an optimally configured EEW 

system. 

Theoretical Performance of ElarmS and a Single Station Within 

the Current Network

Given the current inventory of seismometers on the Island of Hawaiʻi and current infrastructure 

latencies, we can estimate the theoretical warning times of the ElarmS algorithm and compare it to 

having a single-station algorithm implemented at a critical facility. As a reminder, ElarmS requires a 

minimum of four stations to detect an earthquake, while the single-station algorithm only requires one 

station at the critical site (an array may also be deployed at the site). We consider two source depths, a 

shallow source (approximately 6 mi [10 km] below surface) to simulate the décollement responsible for 

the 1868 M7.9 and 1975 M7.7 earthquakes and a deep source (approximately 25 mi [40 km] below 
13

surface) to simulate mantle earthquakes similar to the 2006 M6.7 Kīholo Bay earthquake. The 

calculation of the single-station warning time assumes that there is one station located at the critical 

facility that triggers an alarm without need of telemetry and with no contribution from the existing 

network. All theoretical ElarmS warning times assume the current inventory of installed stations and 

that those stations are fully operational with data delayed by current telemetry latency and half of the 

current packet length. We assume a processing time of 0.5 seconds for both methods and that the singlestation algorithm requires a minimum of three seconds of seismic data to issue an alert. Here, we define 

the warning time as the difference between the arrival of the s-wave and the time of detection. For the 

two source depths we will consider theoretical warning times to Hilo, Kailua-Kona, Honolulu, and the 

observatories at the summit of Mauna Kea.

Hilo is the county seat of Hawaiʻi County and the Island of Hawaiʻi’s most densely populated 

area. Hilo possesses a critical seaport, an airport, a hospital, a Civil Defense facility, and 

telecommunications and power infrastructure for the entire island. ElarmS theoretical warning times to 

Hilo from shallow sources range from zero seconds on Kīlauea’s lower East Rift Zone at Cape 

Kumukahi, to 15 seconds for shallow sources located near South Point (fig. 8). Damaging shallow 

earthquakes are most likely to occur under the south flanks of Kīlauea and Mauna Loa and the west 

flanks of Mauna Loa and Hualālai so other areas are not discussed, though they are included in the 

maps. The blind zone for a shallow earthquake source with the current network configuration and 

latencies is geographically large. A critical facility in Hilo with a single-station algorithm implemented 

on one station located at the facility would potentially receive as much as 2 seconds of additional 

warning time for a shallow earthquake offshore to the north or east, but a single station system has 

similar warning times as a network system for shallow sources elsewhere on the Island of Hawaiʻi.

ElarmS theoretical warning times to Hilo for deep earthquakes range from 10–14 seconds for 

earthquakes on the west side of the Island of Hawaiʻi to less than 2 seconds for deep earthquakes near 

Laupāhoehoe and Glenwood. The blind zone for deep earthquake sources is a large area extending 

radially up to 30 km from downtown Hilo. For deep earthquakes sources on the east side of the Island of 

Hawaiʻi, a single station implementation at a critical facility would see less than 2 additional seconds of 

warning, with more warning for deep earthquakes occurring offshore of Hilo to the northeast.

Kailua-Kona is the second-most-populous area on the Island of Hawaiʻi and a hub for tourism.

Critical facilities include an international airport and many large hotels. ElarmS warning times in 

Kailua-Kona are relatively large for shallow earthquakes on the south flanks of Mauna Loa and Kīlauea 

and deep earthquake sources on the east side of the Island of Hawaiʻi (fig. 8). There could also be up to 

3 seconds of additional warning for earthquake sources of all depths at critical facilities in Kailua-Kona 

that implement a single-station approach. For shallow sources on the south flank of Mauna Loa and 

Kīlauea, ElarmS warning times range from 11 seconds near South Point to 20 seconds at the east end of 

Kīlauea’s East Rift Zone. For deep earthquake sources on the east side of the Island of Hawaiʻi, ElarmS 

warning times for Kailua-Kona are between 6 and 20 seconds. There is a large blind zone that 

encompasses nearly all of Hualālai Volcano and Kailua-Kona, including the epicenter of the 1929 M6.1 

earthquake and the 2006 M6.7 Kīholo Bay earthquake. Critical facilities using a single-station approach

in Kailua-Kona may gain less than 2–3 seconds of additional warning time for deep earthquake sources 

that occur to the west of the summit of Hualālai. There is no significant difference in warning times 

between a single station approach and a network approach for deep earthquake sources on the east part 

of the Island of Hawaiʻi.
14

Figure 8. Warning time to Hilo, Kailua-Kona and the summit of Mauna Kea from different source areas considering the 

existing earthquake early warning stations and latency. Black triangles are existing earthquake early warning stations.

Clear triangles represent non-realtime accelerometers or short period instruments, neither of which can be used for 

earthquake early warning. Black contours are warning times in seconds using an ElarmS algorithm that requires four

stations for earthquake detection. Red contours are the additional warning time of a single-station system assuming a 

single station placed at a critical facility at the target area. Shaded pink area is the ElarmS blind zone. A, Warning times to 

Hilo from sources at a depth of 6 mi (10 km) to simulate a décollement source. B, Warning times to Hilo from sources at a 

depth of 25 mi (40 km) to simulate a mantle source. C, Warning times to Kailua-Kona from sources at a depth of 6 mi (10 

km) to simulate a décollement source. D, Warning times to Kailua-Kona from sources at a depth of 25 mi (40 km) to 

simulate a mantle source. E, Warning times to the summit of Mauna Kea from sources at a depth of 6 mi (10 km) to 

simulate a décollement source. F, Warning times to the summit of Mauna Kea (MKO) from sources at a depth of 25 mi (40 

km) to simulate a mantle source.
15

Figure 8. —Continued
16

Figure 8. —Continued
17

The observatories at the top of Mauna Kea have instrumentation that is highly susceptible to 

shaking, as shown by damage caused during the 2006 Kīholo Bay earthquake (McAvoy, 2006). The 

current station coverage around Mauna Kea is relatively sparse, which leads to relatively short warning 

times and a large blind zone. For shallow earthquake sources on the south flanks of Kīlauea and Mauna 

Loa, ElarmS warning times to Mauna Kea range from 4 seconds near the summit of Mauna Loa to 14 

seconds at South Point (fig. 8). For shallow earthquake sources to the west of Hualālai, warning times to 

the observatories range from 2 to 6 seconds. The blind zone for shallow sources is large; however, it 

encompasses an area unlikely to have damaging shallow earthquakes (Klein and others, 2001). A critical 

facility with a single-station algorithm implemented upon Mauna Kea stands to gain less than 2 seconds 

for shallow sources within the ElarmS blind zone, so there is no benefit for shallow sources under 

Kīlauea or Mauna Loa. For deep earthquake sources on the north part of the Island of Hawaiʻi, ElarmS 

has the potential for warning times of up to 4 seconds for a facility at the top of Mauna Kea. The blind 

zone for deep earthquake sources is a geographic area extending radially from Mauna Kea for 30 to 50 

km. There have been 11 deep earthquakes between M4 and M5 that have occurred within the blind zone 

since 1960 and 3 M≥6 earthquakes since 1881 (fig. 2; fig. 8). A critical facility on Mauna Kea using a 

single-station system will receive up to 2 seconds of additional warning time for earthquakes that occur 

within the ElarmS blind zone. A single-station algorithm could also give between 0 and 2 seconds of 

additional warning for most deep earthquake sources on the west part of the Island of Hawaiʻi. For most 

of the earthquakes occurring on the south flanks of Kīlauea and Mauna Loa, a single-station algorithm 

would provide no more warning than ElarmS for deep earthquake sources when considering critical 

facilities atop Mauna Kea.

Honolulu is the final locale that we consider because of its critical infrastructure and large 

population. The seismic hazard on O‘ahu due to large earthquakes on the Island of Hawaiʻi is severe 

enough to consider potential warning times to Honolulu, especially considering the disruption caused in 

Honolulu by the 2006 M6.7 Kīholo Bay earthquake, which included widespread power outages (Reyes, 

2006). Theoretical ElarmS warning times for Honolulu are similar between shallow and deep 

earthquake sources and range from 40 seconds for earthquakes on the north part of the Island of Hawaiʻi

and 75 seconds for damaging earthquakes occurring on the most distal parts of Kīlauea’s East Rift Zone 

(fig. 9). For critical facilities in Honolulu, a single-station algorithm may provide up to 2 seconds of 

additional warning for earthquakes occurring within the ElarmS blind zone, but there is no benefit to 

using a single-station algorithm to warn against shaking from earthquakes on the Island of Hawaiʻi (fig. 

9).
18

Figure 9. Warning times to Honolulu from different source areas considering the existing earthquake early warning 

stations and data latency. Black triangles are existing earthquake early warning stations. Clear triangles represent nonreal-time accelerometers or short-period instruments, neither of which can be used for earthquake early warning. Black 

contours show warning times, in seconds, using an ElarmS algorithm that requires four stations for an earthquake 

detection. Red contours are the additional warning times of a single-station system assuming one station installed at a 

critical facility in Honolulu. Shaded pink area is the ElarmS blind zone. A, Warning times to Honolulu from sources at a 

depth of 6 mi (10 km) to simulate a décollement source. B, Warning times to Honolulu from sources at a depth of 25 mi 

(40 km) to simulate a mantle source.
19

Testing of ElarmS Within the Current Network

To better understand how an EEW system might work within the State of Hawaii, we 

implemented the ElarmS portion of the ShakeAlert system for a 10-month test of performance. We used 

configurations adopted from the Pacific Northwest Seismic Network (PNSN) with little tuning. There 

were three main goals for the test:

1. To understand the performance of the ElarmS system given the current seismic network and 

diverse seismicity on the Island of Hawaiʻi.

2. To test the processing times and alarm times for ElarmS.

3. To understand what needs to be tuned, adjusted, or added to decrease alarm times and minimize 

false triggers.

The performance of the ElarmS component of ShakeAlert is highly dependent on the magnitude 

cutoffs that we consider. Here we consider only earthquakes over magnitude 3 as defined by the ANSS 

earthquake catalog generated by HVO. During the test, there were 35 ElarmS alerts for earthquakes 

greater than M3. The events were mostly on the southern half of the Island of Hawaiʻi, with four 

earthquakes occurring near Mauna Kea and one earthquake significantly offshore to the northeast. No 

earthquakes greater than M3 occurred on the west coast of the Island of Hawaiʻi during our test. There 

were also seven false alarms from ElarmS that had no associated earthquake in the earthquake catalog.

Two of the false alarms suggested earthquakes well off the Island of Hawaiʻi to the south and did not 

forecast strong ground shaking. The five other false alarms were each related to a rockfall into the active 

lava lake at the summit of Kīlauea. Though not a source of shaking hazard, the false alarms did forecast 

strong shaking in some regions because of artificially high magnitudes. There were no teleseisms 

(distant earthquakes) that triggered a false alarm during this testing period.

Processing times between the last contributing trigger and the ElarmS alarm ranged from 2 to 6

seconds for earthquakes equal to or greater than M3. The median time was 3.3 seconds, which includes

latencies in digitizer processing and telemetry, so the actual ElarmS processing time is much less.

Locations of earthquakes calculated by ElarmS have a median error of 4.6 km compared to the reviewed 

earthquake catalog locations. The magnitude calculated by ElarmS has a median error of -0.3 magnitude 

units compared to the actual value calculated in the HVO earthquake catalog.

The location and magnitude calculations made by ElarmS during the testing period are

reasonably accurate for the Island of Hawaiʻi, but the number of false alarms was too high and could be 

reduced. One way to do so is to reduce the geographical area in which an EEW system detects large 

earthquakes. For instance, by only distributing alarms for earthquakes that are within approximately 20 

km or so of the south and east coasts, we could cut down on the number of false triggers, some of which 

occurred off the coast and outside of the seismic network. The actual distance cutoff could be a topic of 

future research. There must also be a provision to exclude rockfalls in the Kīlauea summit area. The 

rockfalls tend to have imprecise locations in ElarmS that cover a broad region of Kīlauea’s summit 

caldera and south flank so a simple geographic exception is probably not sufficient. Future work could

to be done to better understand how to quickly distinguish the rockfall events from regular earthquakes.

Steps Toward Full EEW Implementation

While the implementation of a single-station EEW system is relatively straightforward, as ready

commercial kits are available, the full implementation of a network-based EEW system is more 

complicated because it would involve the purchase and installation of new equipment and additional 

staffing to install, develop, and maintain the EEW system. The following discussion assumes that we 

will use ShakeAlert as the network-based EEW system of choice. We rely heavily on the experience of 

the consortium of organizations that are currently implementing ShakeAlert on the West Coast of the 

United States to guide our estimate of what would be required to implement an EEW system in Hawaiʻi.
20

One way to improve warning time is to increase the density of stations. Kuyuk and Allen (2013) 

suggest that average station spacing of stations on the order of 10–20 km is optimal, because spacing 

more dense than this offers negligible increases in warning time. The current station spacing for the 

Island of Hawaiʻi is <40 km, with three pockets of <10 km spacing around Kīlauea, Mauna Loa, and 

Hilo (fig. 6). The north and west sides of the island are clear targets for additional stations.

Alicia Hotovec-Ellis and coworkers (unpub. data) have developed a methodology to objectively 

target optimal locations to add stations based on improvement in warning time, seismic hazard, and 

station density. Specifically, it identifies sparse areas in the network with high seismic hazard that 

would experience the greatest increases to warning time. Hotovec-Ellis assigns such places a high 

“upgrade score,” and the highest scores are centered on the west coast of Hawaiʻi, north and south of 

Kailua-Kona (fig. 10). High scores coincide with several existing stations that have either triggered 

records or short-period seismometers (sensitivity >10s); those stations are not appropriate for EEW 

systems, but could be upgraded to include EEW-ready instrumentation. Such HVO-owned stations are 

favored for upgrades because the costs are less than establishing a station from scratch. The three best 

candidates for upgrades are two USGS NSMP stations on the northwest coast and an HVO station on 

the west coast near Captain Cook (table 1).

Assuming those three stations are added to the EEW network, the next best candidates are an 

HVO station on the southwest coast, a former NetQuakes site on the north coast, and three new stations 

(table1). Two more upgrades to NSMP sites and three upgrades to HVO sites round out the 

recommended improvements to the seismic network, which total 10 station upgrades and 3 new station 

installations (fig. 10).

Further upgrades beyond these 13 sites would not significantly affect warning time, assuming 

four stations are required for an initial warning. However, additional stations would improve the 

resilience of the network to station outages. Hotovec-Ellis and others (unpub. data) simulated a single 

station outage by increasing the number of stations required to render a warning to 5. The results show 

that the areas most susceptible to outages: north of Mauna Kea where there are no existing stations, and 

south of Hilo in the vicinity of a NSMP station. If all of the stations noted in figure 10 and table 1 are 

upgraded or installed, the new average station spacing is reduced to <20 km for nearly the entire island, 

with exceptions on the north, south, and east tips (fig. 10). This new station spacing would be on par 

with EEW networks in Japan and California. The State of Hawaii is geographically limited, as real-time 

broadband seismometers and accelerometers only exist on land and thus it is unlikely, given current 

technology, that an offshore earthquake could be optimally detected by an EEW system without 

resorting to extremely expensive surface-tethered ocean bottom seismometers.

Improvements to the seismic network around the volcanoes is ongoing, especially along the rift 

zones of Mauna Loa and Kīlauea as part of the National Volcanic Early Warning System (NVEWS; 

Ewert and others, 2005; Thelen, 2014). New stations installed as part of NVEWS stand to improve the 

density of stations and robustness of alarms to station outages in certain regions, but does not directly 

change the priority of the station upgrades noted here because none of the sites proposed in this study 

are near enough to the active volcanoes.

Beyond improving the station distribution of the network, major improvements to warning times 

may be realized by decreasing the latency of the data that is received at the datacenter. One simple 

change that could be made is to reduce the size of packets that are digitized on site. The current 

digitizers used in most of the HVO-operated seismic network have packet sizes between 5 and 9 

seconds. By replacing the existing digitizers with ones that use 1-second packets, we can quickly cut 

overall latency. Such an improvement will require an upgrade of 30 existing stations (strong motion or 

broadband sites) within the HVO network. New or proposed upgrades should also include the shortpacket digitizers.
21

Figure 10. A, Map of proposed station upgrades. Warm colors indicate an upgrade score 

determined using methodology from Hotovec-Ellis and others (unpub. data). Higher upgrade

scores indicate areas where upgrading stations would provide the most additional warning 

time to areas of high seismic hazard. B, Contour map of station density (distance to the 

nearest four stations) with new stations included based on the method of Kuyuk and Allen 

(2013). Clear triangles represent existing stations that are not sufficient for use in earthquake 

early warning. Black triangles represent existing earthquake-early-warning-ready stations.

Circles indicate stations identified for upgrades in instrumentation and telemetry or entirely 

new station locations.
22

Table 1. List of instrument sites that could be upgraded to contribute to an earthquake early 

warning network, listed by descending upgrade score (Modified from Hotovec-Ellis and others,

unpub. data).

[The locations are shown as black circles in figure 10. In the first column, Name refers to the name of the station, while the 

Net refers to the operator: NP, National Strong Motion Program; HV, Hawaiian Volcano Observatory]

Name.Net Latitude Longitude Locale

2847.NP 19.91 -155.88 Waikoloa

2832.NP 20.08 -155.46 Honokaʻa

CACD.HV 19.48 -155.11 Captain Cook

KAAD.HV 19.26 -155.87 Kaʻapuna

HGC.HV 19.87 -155.11 Honomū

New Install 19.69 -155.27 Upper Waiakea

New Install 19.78 -156.03 Kona Airport

New Install 19.08 -155.90 Miloliʻi

2846.NP 19.55 -155.11 Mountain View

KKUD.HV 19.89 -155.34 Keanakolu

WAID.HV 19.86 -155.66 Waikiʻi Ranch

PPLD.HV 19.15 -155.46 Puʻu Pili

2826.NP 20.23 -155.80 Kapaaʻu

Total: 13 (3 new installs, 10 station upgrades)

The speed and reliability of telemetry may also be considered. Upgrading digitizers will also 

reduce the time it takes to transmit the data across the existing telemetry network. Based on current 

telemetry performance, we may see telemetry latencies reduced to around 1 second, compared to the 

current range of 1.8 to 3.8 seconds. All of the EEW-eligible stations operated by HVO traverse the same 

telemetry network, which has been extremely robust. Even so, diversifying the telemetry used by a 

subset of the HVO-operated sites with cell modems would add communication capability in the case of 

a catastrophic failure of the HVO telemetry network. Stations that transmit data over cell modems

should be geographically distributed relative to each other and to existing PTWC sites, which already 

receives data via cell modem. We have not specified which sites might be the best candidates for this 

telemetry upgrade, as the cell phone signal strength is not well characterized on the Island of Hawaiʻi.

Assuming the entirety of station upgrades are completed, new stations are installed, and latencies 

are ideally minimized, a best-case scenario for ElarmS performance can be calculated (figs. 11 and 12,

table 2). The overall effects for critical facilities in Hilo, Kailua-Kona, and telescopes at the top of 

Mauna Kea would be a reduction or elimination of the ElarmS blind zone and improvement of ElarmS 

warning times of shallow earthquakes to about 2–4 seconds (fig. 11). Deep earthquake ElarmS warning 

times would also be improved, especially near the edges of the idealized blind zone. Additional warning 

times provided by a single-station system, as compared to an idealized ElarmS system, would also be 

reduced significantly if not eliminated (fig. 11). For critical sites in Honolulu, there would be a 2–5 

second increase in ElarmS warning times for sources on the Island of Hawaiʻi (fig. 12). Overall reduced 

latencies reduce the ElarmS blind zone in the vicinity of Honolulu.
23

Figure 11. Warning time to Hilo, Kailua-Kona, and the summit of Mauna Kea from different source areas, assuming

incorporation of all the proposed upgrades to stations and telemetry. Black triangles are existing earthquake early warning 

stations. Clear triangles represent non-real time accelerometers or short period instruments, neither of which can be used 

for earthquake early warning. Numbers on black contours are warning times, in seconds, using an ElarmS algorithm that 

requires four stations for an earthquake detection. Red contours are the additional warning time received by a singlestation system, assuming one station placed at a critical facility at the target area. Shaded pink area is the ElarmS blind 

zone. A, Warning times to Hilo from sources at a depth of 6 mi (10 km) to simulate a décollement source. B, Warning 

times to Hilo from sources at a depth of 25 mi (40 km) to simulate a mantle source. C, Warning times to Kailua-Kona from 

sources at a depth of 6 mi (10 km) to simulate a décollement source. D, Warning times to Kailua-Kona from sources at a 

depth of 25 mi (40 km) to simulate a mantle source. E, Warning times to the summit of Mauna Kea from sources at a 

depth of 6 mi (10 km) to simulate a décollement source. F, Warning times to the summit of Mauna Kea from sources at a 

depth of 25 mi (40 km) to simulate a mantle source.
24

Figure 11. —Continued
25

Figure 11. —Continued
26

Figure 12. Warning time to Honolulu from different source areas, assuming incorporation of all the proposed upgrades to 

stations and telemetry. Black triangles are existing earthquake early warning stations. Clear triangles represent non-real

time accelerometers or short period instruments, neither of which can be used for earthquake early warning. Numbers on 

black contours are warning times, in seconds, using an ElarmS algorithm that requires four stations for an earthquake

detection. Red contours are the additional warning time received by a single-station system, assuming one station placed 

at a critical facility in Honolulu. Shaded pink area is the ElarmS blind zone. A, Warning times to Honolulu from sources at 

a depth of 6 mi (10 km) to simulate a décollement source. B, Warning times to Honolulu from sources at a depth of 25 mi 

(40 km) to simulate a mantle source.
27

Table 2. Current and idealized theoretical ElarmS warning times to areas of high population or 

critical infrastructure on the Island of Hawaiʻi for some notable historical earthquakes. See the 

earthquakes with stars after the annotations in figure 2 for the earthquake.

Warning times (in seconds)

1868 M7.9

Ka‘ū

1929 M6.5

Hualālai

1973 M6.2

Honomū

1975 M7.2

Kalapana

2006 M6.7

Kīholo Bay

Target Current Ideal Current Ideal Current Ideal Current Ideal Current Ideal

Hilo 12 14 11 14 0 2 5 7 11 15

KailuaKona10 12 0 0 13 15 18 20 0 4

Mauna Kea 

summit

11 14 2 6 2 5 11 14 2 6

Honolulu 67 70 51 55 60 62 71 74 45 47

The robustness of the datacenter is also an important consideration for an EEW system.

Currently, all data are received and analyzed at the U.S. Geological Survey’s Hawaiian Volcano 

Observatory. While there are redundancies in place at HVO that protect against some failure modes, 

having a single location to analyze and distribute data is not ideal for a system that requires high

availability. Recently, HVO completed a direct connection to infrastructure co-located with the Pacific 

Tsunami Warning Center at Ford Island on the Island of O‘ahu, using the U.S. Coast Guard’s ʻĀnuenue

network. This new connection provides HVO with a redundant, independent, and extremely reliable

connection to O‘ahu in the case of a local communications failure at HVO. In addition, HVO is 

currently testing hardware to establish a redundant offsite backup for the HVO seismic network data 

processing and dissemination at Ford Island. To make both datacenters more reliable for the operation 

and distribution of an EEW system, existing servers may need to be upgraded and networking 

components (radios, switches, routers) be upgraded, and spare parts could be purchased so that 

downtime is minimized.

An effective EEW system also requires a level of maintenance that cannot be met with the 

current staff at HVO. Addressing this deficiency involves two steps: first, the hiring of operational staff 

to meet the needs of the current real-time acquisition and analysis software; and, second, the hiring of 

operational staff to support the high-availability requirements, development, and maintenance of the 

new EEW system. The first step, supporting the current real-time network operations that feed data into 

the EEW system, is a critical piece that would strengthen the foundation of the entire EEW system; we 

estimate that HVO will need an additional two IT positions and part of a data analyst position. The 

second step, properly staffing HVO for the maintenance, tuning, and development of an EEW system to

ensure that alarms have both low latency and high accuracy, will likely require at least six additional 

positions. These six new hires would include a program manager, an EEW-dedicated research scientist, 

a field technician, two IT support personnel, an outreach coordinator, and part of a data analyst position.

With this staffing profile in place, HVO would have the best opportunity to provide accurate and timely 

warnings of earthquake shaking with an absolute minimum of system downtime.

ElarmS Compared to a Single-Station Approach

In general, a networked approach to EEW (for example, ShakeAlert/ElarmS) has the advantage 

of a more reliable and accurate warning than a single station, but comes at the cost of a potentially large 

blind zone unless the network and telemetry are optimized. A single station (or small array) co-located 

with processing at a site of interest may provide a few seconds of warning within the blind zone by 
28

bypassing the delay from p-wave travel time to multiple stations plus telemetry and processing. 

However, single-station approaches are more susceptible to noise and, therefore, false alarms. 

Sophisticated single-station algorithms (for example, PreSEIS OnSite; Böse and others, 2012) can 

utilize artificial neural networks with training datasets to discriminate noise from earthquakes, and 

provide estimates of magnitude, epicentral distance, and peak ground velocity (PGV). The pool of 

earthquakes that could be used for a training dataset for Hawaiʻi would be biased heavily by earthquakes 

on the southern side of the island, and would have limited observations at short epicentral distances 

from infrastructure at Hilo, Kailua-Kona, and Mauna Kea, where the single-station approach would give 

the most additional warning. A simpler approach could be to use a threshold of peak ground 

displacement in the p-wave (Pd). Wu and Kanamori [2008] suggest that “if Pd exceeds 0.5 cm, the PGV 

at the site most likely exceeds the damaging level, i.e., 20 cm/s.”

In both cases, data following the initial p-wave trigger must be analyzed, and the amount of 

additional warning time from a single station compared to the networked approach is heavily dependent 

on this analysis window. For the threshold approach, a shorter, expanding window may lead to a faster 

warning, but perhaps only by a few seconds at best. The blind zone for the single-station approach is 

therefore never zero for shallow earthquakes, and is only slightly smaller than what the current network 

can provide with these conservative estimates of single-station warning time. With a fully optimized 

ShakeAlert system, such as proposed here, warning times are typically longer than a single-station 

approach for most sources to most population centers (figs. 11 and 12, table 3).

Table 3. Theoretical warning times to areas of high population or critical infrastructure on the 

Island of Hawaiʻi, comparing an idealized ElarmS system and a single-station approach (called 

“local” below) for some damaging earthquakes of note.

[See the earthquakes with stars after the annotations in figure 2 for the earthquake location. A value of zero indicates that the 

earthquake is within the blind zone for that particular locale]

Warning times (in seconds)

1868 M7.9

Ka‘ū

1929 M6.5

Hualālai

1973 M6.2

Honomū

1975 M7.2

Kalapana

2006 M6.7

Kīholo Bay

Target ElarmS Local ElarmS Local ElarmS Local ElarmS Local ElarmS Local

Hilo 14 5 14 5 2 1 7 2 15 7

KailuaKona12 5 0 0 15 7 20 7 4 2

Mauna Kea 

summit

14 5 6 2 5 2 14 5 6 3

Honolulu 70 28 55 23 61 27 74 30 47 21

Summary

Earthquake early warning has the potential to give seconds of warning of strong shaking to 

individuals, private companies, utilities, and municipalities. In the State of Hawaii, the implementation 

of a network approach to EEW, such as ShakeAlert, has significant potential benefit to the general 

population and critical infrastructure. The most appropriate approach to an EEW system (single-station 

or network) depends on the goals and available funds for such a project. A company eager to provide 

some level of warning of strong shaking to a critical facility (like a telescope) could implement a singlestation system for low cost but may have to tolerate false alarms. If the goal is to warn a larger 

population (including critical facilities) or to provide as much warning as possible, then a network 

approach such as ShakeAlert may be most appropriate. The costs of a fully implemented network 
29

solution such as ShakeAlert is higher, but the number of false alarms are reduced, the warning longer, 

and the impact broader. Given HVO’s current role in statewide earthquake monitoring, its existing 

infrastructure and continued efforts toward improving redundancy, HVO could be an appropriate 

facility to implement a network-based EEW system. One hybrid or phased approach for critical facilities 

would be to implement a single-station system initially to provide some level of protection while a 

network-based EEW system is built.

References Cited

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Letters, v. 36, no. 5, L00B08, doi:10.1029/2008GL036766.

Böse, M., Hauksson, E., Solanki, K., Kanamori, H., Wu, Y.-M., and Heaton, T.H., 2009, A new trigger 

criterion for improved real-time performance of on-site earthquake early warning in southern 

California: Bulletin of the Seismological Society of America, v. 99, no. 2A, p. 897–905, 

doi:10.1785/0120080034.

Böse, M., Heaton, T.H., and Hauksson, E., 2012, Rapid estimation of earthquake source and groundmotion parameters for earthquake early warning using data from a single three-component broadband 

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750, doi:10.1785/0120110152.

Burkett, E.R., Given, D.G., and Jones, L.M., 2014, ShakeAlert—An earthquake early warning system 

for the United States West Coast (ver. 1.1, June 2016): U.S. Geological Survey Fact Sheet 2014–

3083, 4 p., doi:10.3133/fs20143083.

Crosson, R.S., and Endo, E.T., 1982, Focal mechanisms and locations of earthquake in the vicinity of 

the 1975 Kalapana earthquake aftershock zone 1970-1979: implications for tectonics of the south 

flank of Kilauea Volcano, Island of Hawaii: Tectonics, v. 1, p. 495-542.

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