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Faults & earthquakes

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At least 1,549 records · Page 86Linked to original sources

USGS2001

GPS constraints on M 7-8 earthquake recurrence times for the New Madrid seismic zone

Newman et al. ( 1999 ) estimate the time interval between the 1811–1812 earthquake sequence near New Madrid, Missouri and a future similar sequence to be at least 2,500 years, an interval significantly longer than other recently published estimates. To calculate the recurrence time, they assume that slip on a vertical half-plane at depth contributes to the current interseismic motion of GPS benchmarks. Compared to other plausible fault models, the half-plane model gives nearly the maximum rate of ground motion for the same interseismic slip rate. Alternative models with smaller interseismic fault slip area can satisfy the present GPS data by having higher slip rate and thus can have earthquake recurrence times much less than 2,500 years.

Arkansas, Illinois, Kentucky, Missouri, Tennessee↗

USGS2019

Preliminary report on engineering and geological effects of the July 2019 Ridgecrest earthquake sequence

The Ridgecrest Earthquake sequence included a foreshock event on July 4 2019 (M6.4) and a M7.1 mainshock event on July 5 2019. These events occurred in the Eastern California Shear Zone, near Indian Wells Valley, south of China Lake and west of Searles Valley. GEER has partnered with several organizations to collect perishable data and document the important impacts of these events, including the US Geological Survey, the California Geological Survey, the US Navy, the Southern California Earthquake Center, and local utilities. Critical geotechnical features of this event are extensive left-lateral (M6.4 event) and right-lateral (M7.1 event) surface ruptures over fault segments of variable complexity and width as well as across extensional and compressive step-over zones. We also document lifeline performance at fault crossings (gas, water, electrical), mainshock slip and afterslip, liquefaction and lateral spreading features, and liquefaction effects on structures. These effects are documented using field (ground) mapping and aerial imagery that will support subsequent development of high-resolution digital elevation models. Over 750 ground motions were recorded from the foreshock and mainshock alone, with many additional aftershock records. The data demonstrate significant impacts of site response and rupture directivity on ground motion attributes.

Report↗

USGS1967

The Parkfield-Cholame, California, earthquakes of June-August, 1966; instrumental seismic studies

U.S. Geological Survey instrumental seismic studies in the Parkfield-Cholame area consist of three related parts that were undertaken as pilot studies in a program designed to develop improved tools and concepts for investigating the properties and behavior of the San Andreas fault. These studies include: 1. The long=term monitoring of the seismic background on the San Andreas fault in Cholame Valley by means of a short-period Benioff seismograph station at Gold Hill. 2. The investigation of the geometry of the zone of aftershocks of the June 27 earthquakes by means of a small portable cluster of short-period, primarily vertical-component seismographs. 3. The seismic-refraction calibration of the region enclosing the aftershock source by means of three short reversed refraction profiles and a "calibration shot" near the epicenter of the main June 27 earthquake. This brief report outlines the work that has been completed and presents some preliminary results obtained from analysis of records from Gold Hill and the portable cluster.

California↗

USGS2008

Shear wave structure of Umbria and Marche, Italy, strong motion seismometer sites Affected by the 1997-98 Umbria-Marche, Italy, earthquake sequence

A long sequence of earthquakes, eight with magnitudes between 5 and 6, struck the Umbria and Marche regions of central Italy between September 26, 1997 and July 1998. The earthquake swarm caused severe structural damage, particularly to masonry buildings, and resulted in the loss of twelve lives and about 150 injuries. The source of the events was a single seismogenic structure that consists of several faults with a prevailing northwest-southeast strike and crosses the Umbria-Marche border. The focal mechanism of the largest shocks indicates that the events were the product of shallow extensional normal faulting along a NE-SW extension perpendicular to the trend of the Apennines. The network of analog seismometer stations in the Umbria and Marche regions recorded motions of the main September and October 1997 events and a dense array of mobile digital stations, installed since September 29, recorded most of the swarm. The permanent national network Rete Accelerometrica Nazionale (RAN) is administered and maintained by Dipartimento delle Protezione Civile (DPC: Civil Protection Department); the temporary array was managed by Servizio Sismico Nazionale (SSN) in cooperation with small agencies and Universities. ENEA, the operator of many seismometer stations in Umbria, is the public Italian National Agency for New Technologies, Energy and the Environment. Many of the temporary and permanent stations in the Italian seismic network have little or no characterization of seismic velocities. In this study, we investigated 17 Italian sites using an active-source approach that employs low frequency harmonic waves to measure the dispersive nature of surface waves in the ground. We used the Spectral Analysis of Surface Wave (SASW) approach, coupled with an array of harmonic-wave electro-mechanical sources that are driven in-phase to excite the ground. An inversion algorithm using a non-linear least-squares best-fit method is used to compute shear wave velocities for up to 100 meters of the soil column. A draft report was published in the summer of 2008, followed by a comment period, lengthy discussions with Italian colleagues, and improved knowledge of the subsurface at the sites from soil logs. Four of the sites were reprocessed in order to correct issues with phase unwrapping of the field dispersion curves that complicated the velocity profile calculations at the lowest velocity sites. This report presents the final results from the reprocessing effort.

Open-File Report↗

USGS2012

Logs and data from trenches across and near the Green Valley Fault at the Mason Road site, Fairfield, Solano County, California, 2006-2009

The primary purpose of this report is to provide drafted field logs of exploratory trenches excavated across the Green Valley Fault in 2007 and 2009 that show evidence for four surface rupturing earthquakes in the past one thousand years. The site location and site detail are shown on sheet 1. The trench logs are shown on sheets 1, 2, and 3. We also provide radiocarbon laboratory dates used for chronological modeling of the earthquake history. Sheets 4 and 5 show additional data obtained in 2006–2009 to document data obtained in our studies of the long-term geologic slip rate on the Green Valley Fault. However, that effort ultimately did not prove feasible and no slip rate estimate resulted.

California↗

USGS2014

Photomosaics and event evidence from the Frazier Mountain paleoseismic site, trench 1, cuts 1–4, San Andreas Fault Zone, southern California (2007–2009)

The Frazier Mountain paleoseismic site is located at the northwest end of the Mojave section of the San Andreas Fault, in a small, closed depression at the base of Frazier Mountain near Tejon Pass, California (lat 34.8122° N., long 118.9034° W.). The site was known to contain a good record of earthquakes due to previous excavations by Lindvall and others (2002). This report provides data resulting from four nested excavations, or cuts, along trench 1 (T1) in 2007 and 2009 at the Frazier Mountain site. The four cuts were excavated progressively deeper and wider in an orientation perpendicular to the San Andreas Fault, exposing distal fan and marsh sediments deposited since ca. A.D. 1200. The results of the trenching show that earthquakes that ruptured the site have repeatedly produced a small depression or sag on the surface, which is subsequently infilled with sand and silt deposits. This report provides high-resolution photomosaics and logs for the T1 cuts, a detailed stratigraphic column for the deposits, and a table summarizing all of the evidence for ground rupturing paleoearthquakes logged in the trenches.

California↗

USGS2014

Logs and data from trenches across the Berryessa Fault at the Jerd Creek site, northeastern Napa County, California, 2011-2012

The primary purpose of this report is to provide drafted field logs of exploratory trenches excavated across the Berryessa Fault section of the northern Green Valley Fault (Lienkaemper, 2012; Lienkaemper and others, 2013) in 2011 and 2012 that show evidence for at least one surface-rupturing earthquake in the past few centuries. The site location and site detail are shown on sheet 1. The trench logs are shown on sheets 1, 2, 3 and 4. We also provide radiocarbon ages used for chronological modeling of the earthquake history and a field description of a soil profile in one trench. A formal report based on these logs and data is in preparation.

California↗

USGS1970

Satellite relay telemetry of seismic data in earthquake prediction and control, 1968 and 1969

This report describes the progress of the Satellite Telemetry Earthquake Monitoring Program during the period 1 July 1968 through 30 June 1969. This research was supported by the National Aeronautics and Space Administration under Contract No. R-09-020-011, Task No. 160-75-01-50-10. The project was initiated in FY 1968 to evaluate the applicability of satellite relay telemetry in the collection of seismic data from a large number of dense seismograph clusters laid out along the major fault systems of western North America. Prototype clusters utilizing phone-line telemetry were then being installed by the National Center for Earthquake Research (NCER) in 3 regions along the San Andreas fault in central California; and the experience of installing and operating the clusters and in reducing and analyzing the seismic data from them was to provide the raw materials for evaluation in the satellite relay telemetry project.

Open-File Report↗

USGS1980

A homogeneous stochastic model for earthquake occurrences

The objective of this study is to develop a probabilistic model for earthquake occurrences with temporal and spatial memory. Stochastic processes are used to characterize both the spatial and temporal dependencies of seismic occurrences along a fault. Currently, only homogeneous space and time transitions are considered. The resulting process however is evolutionary and depends on the specific sequence of events over a period of time. The model provides estimates on the cumulative activity of a fault over a future time period. In addition, probabilities of occurrences of individual events along a geologic fault at some specified future time are obtained when a descritized time scale is used. The information from these evaluations is particularly useful in engineering seismic hazard computations and for social and engineering seismic risk assessments.

Open-File Report↗

USGS1997

Volcano and earthquake hazards in the Crater Lake region, Oregon

Crater Lake lies in a basin, or caldera, formed by collapse of the Cascade volcano known as Mount Mazama during a violent, climactic eruption about 7,700 years ago. This event dramatically changed the character of the volcano so that many potential types of future events have no precedent there. This potentially active volcanic center is contained within Crater Lake National Park, visited by 500,000 people per year, and is adjacent to the main transportation corridor east of the Cascade Range. Because a lake is now present within the most likely site of future volcanic activity, many of the hazards at Crater Lake are different from those at most other Cascade volcanoes. Also significant are many faults near Crater Lake that clearly have been active in the recent past. These faults, and historic seismicity, indicate that damaging earthquakes can occur there in the future. This report describes the various types of volcano and earthquake hazards in the Crater Lake area, estimates of the likelihood of future events, recommendations for mitigation, and a map of hazard zones. The main conclusions are summarized below.

Oregon↗

USGS1996

Slip history of the 1995 Kobe, Japan, earthquake determined from strong motion, teleseismic, and geodetic data

Near-source ground motions, teleseismic body waveforms, and geodetic displacements produced by the 1995 Kobe, Japan, earthquake have been used to determine the spatial and temporal dislocation pattern on the faulting surfaces. A linear, least-squares approach was used to invert the data sets both independently and in unison in order to investigate the resolving power of each data set and to determine a model most consistent with all the available data. A two-fault model was used, with a single rupture plane representing faulting beneath Kobe and a second plane representing slip underneath Awaji Island. The total seismic moment is estimated to be 2.4×10 19 Nm (M W 6.9), with rupture partitioned such that about 40% of the slip was relatively deep (5-20 km) and northeast of the epicenter toward Kobe, and about 60% was toward the southwest and shallower (mostly 0-10 km) beneath Awaji Island. Analysis of the slip model indicates that the ground motions recorded within the severely damaged region of Kobe originated from the region of relatively low slip (about 1 m) deep beneath Kobe and not from the shallow, higher slip regions (about 3 m) beneath Awaji Island. Although the slip was relatively low beneath Kobe, the combined effects of source rupture directivity, a short slip duration, and site amplification conspired to generate very damaging ground motions within the city.

Journal of Physics of the Earth↗

USGS1971

Satellite relay telemetry of seismic data in earthquake prediction and control

The Satellite Telemetry Earthquake Monitoring Program was started in FY 1968 to evaluate the applicability of satellite relay telemetry in the collection of seismic data from a large number of dense seismograph clusters laid out along the major fault systems of western North America. Prototype clusters utilizing phone-line telemetry were then being installed by the National Center for Earthquake Research (NCER) in 3 regions along the San Andreas fault in central California; and the experience of installing and operating the clusters and in reducing and analyzing the seismic data from them was to provide the raw materials for evaluation in the satellite relay telemetry project.

Conference Paper↗

USGS2021

California deepwater investigations and groundtruthing (Cal DIG) I: Fault and shallow geohazard analysis offshore Morro Bay

The California Deepwater Investigations and Groundtruthing (Cal DIG) I project focuses on the potential seafloor hazards and impacts of alternative energy infrastructure in the outer continental shelf region offshore of south-central California. This is one of three reports covering a single study area located between Monterey and Point Conception, California in federal waters outside of the State of California three nautical mile limit and in water depths of 400 to 1500 meters. The goal of this report is to provide baseline geologic interpretations of the area for the purpose of improving regional models of shallow geologic hazards and sedimentary processes. Geophysical and geological data from this project will help to address important issues associated with marine spatial planning and potential offshore infrastructure development, such as offshore floating wind turbines. Datasets covered in this report include comprehensive high-resolution sub-bottom (multi-channel and Chirp seismic reflection profiles), seafloor (bathymetry), and sampling (piston, gravity, and vibracore) data collected in 2018-2019 during a series of seven seagoing geological and geophysical surveys. Specifically, this report outlines interpretation of subsurface geologic structure from the geophysical data, details preliminary core analysis results related to fluid, gas, and sediment transport activity, provides interpretations of the current geohazards in the area, and suggests next steps for improving interpretations of geohazard processes. Specific targets of geohazard interest in the study area are geological structures such as faults and folds, seafloor pockmarks within a large field (the Big Sur pockmark field), submarine channels, and mass wasting (slope failure) features. The vast majority of faults and other structures in the study occur within sediment and rock formations we interpret to be pre-Quaternary (older than 2.58 Myr BP), and thus we interpret that these structures are unlikely to present significant current hazard to seabed infrastructure, although we note that the numerous structures mapped in the study area may have the potential to become reactivated. Similarly, we find no new evidence of Holocene (younger than 11,650 years BP) fluid or gas advection in the Big Sur pockmark field. However, such fluid and gas hazards are currently difficult to assess, as additional analyses and sampling of existing core data is needed to better understand pockmark formation processes and potential gas accumulations we have mapped in the subsurface. Mass wasting along the eastern and western edges of the Santa Lucia Bank during earthquakes, as well as sediment transport down the Lucia Chica and San Simeon channels, are among the most significant, although still likely infrequent during the Holocene, hazards to seabed stability in the study area. Further analyses of the existing cores, including radiocarbon dating, stable isotope, and compositional analyses, are again needed to better understand the timing and sources of the numerous sand deposits found throughout the study area, which may have been transported downslope due to mass wasting and/or earthquake shaking processes.

California↗

USGS2019

National earthquake information center strategic plan, 2019–23

Executive Summary Damaging earthquakes occur regularly around the world; since the turn of the 20th century, hundreds of earthquakes have caused significant loss of life and (or) millions of dollars or more in economic losses. While most of these did not directly affect the United States and its Territories, by studying worldwide seismicity we can better understand how to mitigate the effects of earthquakes when they do occur within U.S. borders. Within the U.S. Government, this mandate falls on the U.S. Geological Survey (USGS) National Earthquake Information Center (NEIC), which has the statutory responsibility for monitoring and reporting on earthquakes domestically and globally. The NEIC has been operating since 1966, and throughout its history has been recognized as a world leader for earthquake information. For much of this time, NEIC has been cooperating with a number of regional seismic networks (RSNs) which operate in areas of heightened seismicity in the United States. In 2000, the Advanced National Seismic System (ANSS) was founded as a cooperative umbrella for earthquake-related data collection, analysis, and dissemination in the United States, thereby promoting advanced interoperability between the NEIC and RSN partners. The NEIC also cooperates and coordinates with dozens of global seismic networks. At present (2019), NEIC acquires real-time waveform data from more than 2,000 seismic stations worldwide, contributed from more than 130 seismic networks. Since 2006, the NEIC has operated on a 24-hour, 7-days per week (24/7) basis, and reports on about 30,000 earthquakes per year. Soon after the occurrence of a significant global earthquake, notifications are issued to government representatives, aid agencies, the press, and members of the general public by the Earthquake Notification Service (ENS), electronic feeds, and through the USGS Earthquake Hazards Program (EHP) website. Event-specific web pages provide detailed source parameter information outlining the location and magnitude of the earthquake, including more detailed source characteristics like moment magnitude and focal mechanisms and finite fault solutions. Further, NEIC produces a suite of real-time situational awareness products, including ShakeMap, ShakeCast, Did-You-Feel-It? (DYFI?), and Prompt Assessment of Global Earthquakes for Response (PAGER), to characterize the shaking resulting from the earthquake and the impact it is likely to have on nearby populations and infrastructure. All of these products are ultimately archived in the ANSS Comprehensive Catalog (ComCat), hosted and served by the NEIC. The NEIC also pursues an active research program to improve its ability to characterize earthquakes and understand their hazards. These efforts are all aimed at mitigating the risks of earthquakes to humankind. To maintain its prominent position in earthquake monitoring, the NEIC must continue to evolve, concurrently improving its operations and 24/7 robustness, streamlining services and infrastructure, and keeping pace with research and innovation in the field of seismology. This document outlines how the NEIC might best achieve such goals, by describing specific avenues and opportunities for development in the next five years (2019–23). Several key areas of operational and research focus are identified in this plan as being of the highest importance. First, NEIC must finalize improvements to its regional monitoring capabilities, including the implementation of a variety of improved earthquake detection and association algorithms. One of the most exciting avenues of recent research expansion in earthquake monitoring has involved the use of machine learning; NEIC must explore the benefits of machine learning for improved earthquake detection and source characterization. NEIC also needs to address issues related to the timeliness of earthquake information, exploring the benefits of distributing information as it becomes available, rather than when certain quality criteria are met. To that end, the incorporation of real-time Global Positioning System (GPS) data into the NEIC operational workflow will help improve the speed and accuracy of information for moderate-to-large earthquakes. Finally, NEIC should explore how to further expand and improve the quality and content of the products served during earthquake response efforts, including the generation of new earthquake sequence-specific products, adding an evolutionary component to earthquake information, and continued improvements to earthquake impact products.

Circular↗

USGS1985

Attitude, movement history, and structure of cataclastic rocks of the Flemington Fault results of core drilling near Oldwick, New Jersey

Since 1978, the U.S. Geological Survey (USGS) has cored cataclastic rocks at six localities along border faults of the Early Mesozoic Newark basin in New York and New Jersey. This drilling was done as part of fault definition studies for the USGS Earthquake and Reactor Hazard Programs. The purposes of these studies are to: (1) determine the attitude and location of major faults, (2) assess evidence for recent reactivation, and (3) identify the movement history and depth of formation of the faults. The results of these studies up to 1980 are summarized in Ratcliffe (1980) and a study of a site in Rockland County, N.Y. appears in Ratcliffe 1982). The attitude and movement history of these faults is particularly important because of the possible association of recent low-level seismicity in the New York-New Jersey area with the Ramapo-Flemington fault system (Aggarwal and Sykes, 1978). Previous studies have shown that the Ramapo fault dips to the southeast at angles varying from 70° to 45° and strikes N. 40° E. to N. 10° E. In all of the cored fault zones, the actual contact of hanging-wall and footwall blocks is expressed as a relatively narrow zone, 3 to 8 inches thick, of dark, finely comminuted, fluxionbanded gouge. The intensity of cataclasis decreases rapidly upwards so that rocks 60 ft or so above the fault are not strongly cataclastic. Gneiss, dolostone, and phyllonite in the footwall block are generally weakly deformed more than 30 ft below the fault. Movement sense on the Ramapo fault is largely dip-slip and right-oblique normal faulting. In the summer of 1983, two holes were drilled through the border fault of the Newark basin near Oldwick, New Jersey, in the Gladstone 7.5minute quadrangle. Figure 1A shows the location of the drill site in relation to regional geology and the major faults. The fault drilled in this study connects to the south with the Flemington fault, which trends southwestward across the Newark basin, as shown. To the north, the fault can be traced along the valley that extends towards Mendham, N. J., beyond the limits of exposed Mesozoic rocks, to connect with the Ramapo fault near Morristown N. J. (fig. 1A; Ratcliffe, 1980). For this reason, we use the name "Flemington" for the border fault in the region of the drill site. A detailed map (fig. 1B) shows the local geology along the border fault from Pottersville, N. J. southward to the axis of the Oldwick syncline.

New Jersey↗

USGS2008

WGCEP historical California earthquake catalog

This appendix provides an earthquake catalog for California and the surrounding area. Our goal is to provide a listing for all known M > 5.5 earthquakes that occurred from 1850-1932 and all known M > 4.0 earthquakes that occurred from 1932-2006 within the region of 31.0 to 43.0 degrees North and -126.0 to -114.0 degrees West. Some pre-1932 earthquakes 4 < M < 5.5 are also listed. The completeness of the catalog varies strongly in time and space, in accordance with the locations of population centers and seismic instrumentation. The issue of catalog completeness is covered in depth in Appendix I, where seismicity rates are calculated for the state. The state of California was sparsely populated until the gold rush began attracting waves of migrants in 1848. The regular publication of newspapers did not begin in many locations until 1849 and 1850. Consequently, while the historic occurrence of earthquakes in California has been documented back to the 1700s, the pre-1850 catalog is quite incomplete and most of the earthquakes are poorly constrained. Thus we list the pre-1850 earthquakes in this catalog, but for all seismicity rate calculations performed in Appendix I only the 1850-2006 part of the catalog is used. One known and significant pre-1850 earthquake that is not listed in this catalog is the MW9.0 Cascadia subduction zone earthquake of January 26, 1700 (Satake et al. 2003). This earthquake was primarily off the coast of Oregon and Washington, and we do not list it here because its epicenter may very well have been outside of the California region. Yet the southern tip of this earthquake did extend to Eureka. A repeat of this event could create both a substantial shaking and tsunami hazard in California. Other significant pre-1850 earthquakes, which are listed in the catalog below, include two earthquakes in December of 1812 in Southern California of roughly M 7; at least the first of the pair occurred on the San Andreas Fault (Toppozada et al. 2002), and a June 1838 earthquake that occurred on the San Andreas near San Francisco. Data on the 1838 earthquake is particularily sparse ? we do not even know the day on which it occurred - and magnitude estimates range from M 6.8 (Bakun 1999) to M 7.4 (Toppozada et al. 2002). Earthquake listings from 1850-1932 are generally solved for from historical data sources, with magnitudes and locations determined from felt and damage reports rather than from instrumentation. Most earthquake listings from 1932-2006 are based on instrumental recordings, at least in Southern California. The Northern California seismic network did not produce a full instrumental catalog until 1942 and did not begin routine calculation of magnitudes until late in the 1940s (Uhrhammer et al. 1996). Southern California processed some Northern California events, however, particularly with M > 5, before the Northern California network was online. Some earthquakes from 1900-1932, and particularly from 1910-1932 are also based on instrumental readings, but the quality of the instrumental record and the resulting analysis are much less precise than for later listings. A partial exception is for some of the largest earthquakes, such as the San Francisco earthquake of April 18, 1906, for which global teleseismic records (Wald et al. 1993) and geodetic measurements (Thatcher et al. 1906) have been used to help determine magnitudes.

Open-File Report↗

USGS1976

Physical constraints on sounds generated by very small earthquakes

Vertical vibrations of the ground surface due to elastic waves from an earthquake will generate acoustic pressure waves in the overlying atmosphere. Sufficiently intense vibrations of the ground at frequencies greater than about 20 HZ can produce pressure waves that are within the audible range of many animals, including humans. People in the epicentral region of moderate to large earthquakes, for instance, commonly relate hearing sounds accompanying individual earthquakes (here we exclude sounds associated with mechanical resonances in structures such as houses). Descriptions of these sounds range from the report of distant guns to the rumble of thunder or the rushing of a wind (Davison, 1938; Lanchow Seismological Brigade, Appendix II). In many instances, the sounds are described as starting several seconds before the earthquake is felt. Experimental and theoretical verification that such earthquake sounds are generated by high-frequency ground motion from local earthquakes is based on simultaneous acoustic and seismic recordings recently obtained during a swarm of earthquakes in the Imperial Valley, California (Hill and others, 1976). These results show that for local earthquakes in the magnitude range 2 to-3, audible sounds are generated by the first arriving compressional (P) wave while perceptible shaking begins with the larger but slower shear (S) wave, explaining the reports that "earthquake sounds" are frequently heard several seconds before the earthquake is felt. A commonly proposed explanation for alleged anomalous animal behavior hours to days prior to large earthquakes suggests that animals with acute, high-frequency hearing respond to weak '''ultrasonic" sounds generated by small earthquakes occurring in the epicentral region of the impending event. Such earthquakes are presumably too small to be either felt or heard by humans in the region and too small to be routinely recognized as earthquakes on seismograms recorded on a local seismograph network. Evidence that such "popping and cracking" may occur in the region of an impending earthquake comes from laboratory experiments in which the rate of microfracturing in a rock sample subjected to large stress differences increases dramatically before catastrophic failure of the sample (Scholz, 1968; Stesky, 1975). In this paper we investigate the following question: What are the constraints on earthquake size (fault dimension and displacement) and hypocentral distance (distance from the earthquake focus to a point on the Earth's surface) such that animals noted for their acute hearing might react to the sound generated by the event while the same event would go undetected by humans (either by feeling, hearing, or routine identification on a local seismograph network)? Factors to be considered include: 1) the nature of the displacement spectral amplitudes of elastic waves radiated from an earthquake, 2) the effects of attenuation on the spectral components of elastic (seismic) waves over propagation paths from the focus to the Earth's surface, 3) the appropriate scaling of spectral amplitudes from moderate to very small earthquakes, 4) the coupling of elastic waves in the Earth to acoustic waves in the atmosphere, and 5) the threshold-of-hearing characteristics for various animals, including man. In considering these factors, we will find that, except for extremely small, shallow "earthquakes" (fracture dimension on the order of 10 cm and focal depths on the order of 10 m), acoustic emissions from premonitory fracturing ought to be equally audible to both people and animals in the immediate area of the fracturing.

Open-File Report↗

USGS2025

Phase 1 technical implementation plan for the expansion of the ShakeAlert earthquake early warning system to Alaska

Executive Summary The conference report accompanying the fiscal year (FY) 2022 Consolidated Appropriations Act (Public Law 117–103) for the U.S. Department of the Interior and related agencies directed the U.S. Geological Survey (USGS) to “work with the State of Alaska to develop an implementation plan to be completed within two years in order to put ShakeAlert/Earthquake Early Warning in Alaska” (p. 29). Congress included $1 million in the FY 2022 appropriation to conduct this effort. The USGS Earthquake Hazards Program, along with partner organizations, has developed the ShakeAlert earthquake early warning (EEW) system for the West Coast, which currently operates in California, Oregon, and Washington. The purpose of the system and its alert delivery partners is to reduce the impact of earthquakes and save lives and property by delivering ShakeAlert-powered alerts that are transmitted to the public via mass notification technologies, and by providing more detailed data streams to institutional users and commercial service providers to trigger automated, user-specific, protective actions. ShakeAlert was designed in such a way that it could be expanded to other U.S. regions with high earthquake risk, after the build-out of seismic and geodetic networks to support ShakeAlert in a specified region is completed and the necessary funding is secured for long-term operation and maintenance. When an earthquake occurs, seismic waves radiate from the rupturing fault like waves on a pond. It is these waves that people feel as earthquake shaking and that can cause damage to structures. Using networks of ground-motion sensors and sophisticated computer algorithms, ShakeAlert can detect an earthquake seconds after it begins, calculate its location and magnitude, and estimate the resulting intensity of shaking. Early warnings of impending shaking are then sent to people and systems that may experience damaging shaking, allowing them to take appropriate protective actions. Depending on the user’s distance from the earthquake, alerts may be delivered before, during, or after the arrival of strong shaking. There will almost always be a region near the earthquake epicenter where alerts arrive after damaging shaking has begun. The ShakeAlert system updates its ground-motion estimates as an earthquake grows larger. In response to the FY 2022 congressional direction, the USGS worked with the State of Alaska to devise this implementation plan for ShakeAlert expansion to Alaska. The USGS engaged with the Alaska Division of Homeland Security and Emergency Management (DHS&EM) and the Alaska Division of Geological and Geophysical Surveys (DGGS). A cooperative agreement was awarded to the Alaska Earthquake Center (AEC) at the University of Alaska Fairbanks (UAF) for their contributions to the plan and their work coordinating with other networks in Alaska. The USGS engaged with the Alaska Seismic Hazards Safety Commission (ASHSC) throughout the process. The USGS also held a series of Alaska stakeholder engagements. The process of developing the implementation plan was facilitated by contracted staff from Corner Alliance, which is a government consulting firm. This implementation plan describes the details and estimates the costs for a Phase 1 expansion of the ShakeAlert system to Alaska. A geographically limited Phase 1 goal was chosen that covers the highest risk and most populated areas of Alaska. The areas proposed encompass the State’s main population centers and 90 percent of the State’s population. This Phase 1 design is considered very challenging and ambitious from the viewpoint of network operators. The lessons learned if this plan is implemented could be used to consider subsequent phases to expand EEW beyond Phase 1 in Alaska in the future. ShakeAlert is built on the foundation of the sensor networks and data processing infrastructure of the USGS-led Advanced National Seismic System (ANSS). This implementation plan calls for a total of 450 high-quality, real-time EEW-capable ANSS seismic stations in Alaska: 270 new stations, 160 upgraded stations, and 20 existing stations. These seismic station numbers are based on a station spacing of 10 kilometers (km) in urban areas, 20 km in seismic source areas that endanger population centers, and 40 km in other areas. The associated costs also include support for some EEW-capable global navigation satellite system (GNSS) stations, with a focus on improving warnings for large subduction zone earthquakes. For effective EEW, ShakeAlert requires low-latency, high-availability, robust telemetry links to deliver continuous, real-time data from field stations to the data centers. The Alaska data processing hardware infrastructure would follow the general design for fail-safe operation that is used for the ShakeAlert system on the West Coast. The ShakeAlert architecture uses two independent layers: the production layer for earthquake processing and the alert layer to make alerting decisions and serve alerts to users. This implementation plan includes two geographically separated data centers in Alaska, each with two fully independent production and alert layers using the same system design developed for the West Coast. As of March 2024, the ShakeAlert system is at version 3.0.1, with more advanced versions in the development and testing pipeline. ShakeAlert originally used two algorithms to determine the location and magnitude of earthquakes using seismic data. A third algorithm that can calculate very large magnitudes of very large earthquakes with geodetic data was added in March 2024. ShakeAlert publishes several data and alert products to meet the needs of different users. All messages include the location of the earthquake, either as a point or a line, and its magnitude. Ground-shaking estimates are published in two forms, as ground-motion contours and a map grid. Providing adequate warning time for strong shaking (the “target threshold”) requires sending alerts at a threshold lower than that strong shaking level (the “alert threshold”). The thresholds for public alerting in Alaska would be a joint USGS and State decision. To have the greatest benefit, ShakeAlert-powered alerts would be delivered to institutional users and individuals by all practical pathways. The USGS alert layer can support thousands of institutional users and alert redistributors, but the USGS does not have the mission nor the infrastructure and expertise to perform mass notifications to the public or implement automatic actions for end users of the alerts. To meet this need, ShakeAlert recruits private sector “technology enablers” that have the necessary expertise to develop end-user implementations using EEW alerts with the goal of stimulating an EEW industry. Earthquake early warning alerts are useless if people do not know how to respond to them. Although the alert messages include instructions about what to do (drop, cover, and hold on), alerts are more effective if people have been trained in advance. Messages about ShakeAlert’s capabilities, limitations, and benefits could be integrated with existing earthquake education programs, including State-run programs. Therefore, ShakeAlert would coordinate with both public and private partners and stakeholders through various partnerships and agreements to accomplish consistent and ongoing public earthquake hazard education. The estimated capital cost of completing the computing infrastructure and sensor networks for the Phase 1 ShakeAlert expansion to Alaska is approximately $66 million in 2024 dollars. The annual operation and maintenance cost of the completed system is estimated to be $12 million per year in 2024 dollars when fully built out.

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