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At least 127 records · Page 7Linked to original sources
USGS2018

Preface to the Focus Section on the Collaboratory for the Study of Earthquake Predictability (CSEP): New results and future directions

The Collaboratory for the Study of Earthquake Predictability (CSEP; Jordan, 2006 ) carries out fully prospective tests of earthquake forecasts, using fixed and standardized statistical tests and authoritative data sets, to assess the predictive skill of forecast models and to make objective comparisons between models. CSEP conducts prospective experiments at four testing centers around the world, at which more than 400 models and model versions are currently under evaluation. These models include a range of methods and scales from long‐term global earthquake forecasts to short‐term regional forecasts used for Operational Earthquake Forecasting (OEF). CSEP has also conducted retrospective tests and developed new testing methods in its quest to answer fundamental scientific questions, improve seismic hazard assessments, and develop new forecast methods for OEF.

Seismological Research Letters↗
USGS2018

Development of a geodetic component for the U.S. West Coast Earthquake Early Warning System

An earthquake early warning (EEW) system, ShakeAlert, is under development for the West Coast of the United States. This system currently uses the first few seconds of waveforms recorded by seismic instrumentation to rapidly characterize earthquake magnitude, location, and origin time; ShakeAlert recently added a seismic line source algorithm. For large to great earthquakes, magnitudes estimated from the earliest seismic data alone generally saturate. Real‐time Global Navigation Satellite System (GNSS) data can directly measure large displacements, enabling accurate magnitude estimates for M w 7 + "> M w 7 + events, possibly before rupture termination. GNSS‐measured displacements also track evolving slip and, alone or in combination with seismic data, constrain finite‐fault models. Particularly for large‐magnitude, long‐rupture events, GNSS‐based magnitude and rupture extent estimates can improve updates to predicted shaking and thus alert accuracy. GNSS data processing centers at ShakeAlert partner institutions provide real‐time streams to the EEW system, and three geodetic EEW algorithms have been developed through the ShakeAlert collaboration. These algorithms will undergo initial testing within ShakeAlert’s computational architecture using a suite of input data that includes simulated real‐time displacements from synthetic earthquakes and GNSS recordings from recent earthquakes worldwide. Performance will be evaluated using metrics and standards consistent with those adopted for ShakeAlert overall. This initial assessment will guide method refinement and synthesis of the most successful features into a candidate geodetic algorithm for the ShakeAlert production system. In parallel, improvements to geodetic networks and streamlining approaches to data processing and exchange will ensure robust geodetic data availability in the event of an earthquake.

West coast↗
USGS2018

Sensor suite: The Albuquerque Seismological Laboratory Instrumentation Testing Suite

To standardize parameters used in seismometer testing and calibration and to make these algorithms accessible to the seismological community, we have developed a new seismometer testing software package called Albuquerque Seismological Laboratory (ASL) Sensor Test Suite. This software is written in Java and makes use of Seismological Exchange for Earthquake Data (SEED) format. Our goal is not to be all‐inclusive but instead to focus on a few of the instrumentation tests we view as critical when verifying a sensor’s performance. The tests include self‐noise, relative azimuth, relative gain, and estimation of the poles and zeros. For the self‐noise and the relative azimuth, we also include three‐component versions of these tests to allow for the case of sensors with potentially different orientations (e.g., boreholes). The software has been made available on GitHub with the hope that it will be useful for other seismologists who need to quickly verify various sensor parameters without having to write their own versions of the algorithms. Furthermore, by using a common platform and processing algorithms, it becomes possible to compare results among different tests with similar processing methods being used for both.

Seismological Research Letters↗
USGS2018

Spatiotemporal analysis of the Foreshock-Mainshock-Aftershock sequence of the 6 July 2017 M5.8 Lincoln, Montana, earthquake

A MW 5.8 earthquake occurred on 6 July 2017 at 12.2 km depth, 11 km southeast of Lincoln in west central Montana. No major damage or injuries were reported; however, the widely felt mainshock generated a prolific aftershock sequence with more than 1200 located events through the end of 2017. The Lincoln event is the latest in a series of moderate-to-large earthquakes that have affected western Montana. We characterize the spatiotemporal evolution of the sequence using matched filter detection and multiple-event relocation techniques. Moment tensor solutions and aftershock locations indicate faulting occurred on a 9-km-long NNE-striking, near-vertical, strike-slip fault antithetic to the Lewis and Clark Line, the main through-going fault system. Seismicity primarily occurs between 6 and 16 km depth, consistent with seismicity in the Intermountain Seismic Belt. We estimate a fault rupture area of ~64 km2 and ~30 cm of average fault displacement. We identified four foreshocks in the three days prior to, and 3005 aftershocks in the three weeks following the mainshock. The supplemented catalog frequency-magnitude distribution has a b-value of 0.79 and a minimum magnitude of completeness of 0.7. The overall decay rate is consistent with a modified Omori decay law p-value of 0.76 and c-value of 0.32. This event demonstrates that unmapped faults antithetic to major geologic structures play a role in accommodating regional strain in Western Montana and can host significant earthquakes

Montana↗
USGS2018

Ground motions from induced earthquakes in Oklahoma and Kansas

Improved predictions of earthquake ground motions are critical to advancing seismic hazard analyses and earthquake response. The high seismicity rate from 2009 to 2016 in Oklahoma and Kansas provides an extensive data set for examining the ground motions from these events. We evaluate the ability of three suites of ground‐motion prediction equations (GMPEs)—appropriate for modeling tectonic earthquakes in active crustal and stable continental regions—to reproduce the observed ground motions. Mixed‐effects regressions are used to separate the ground‐motion residuals into bias, between‐event, and within‐event terms. Although the residuals depict differing accuracies in the ability of the three GMPE suites to predict the ground motions, some consistent trends emerge in the period, magnitude, and distance dependence. The trends suggest that aspects of the ground motions from these induced earthquakes are not well modeled by current tectonic GMPEs. Most important, we find evidence for relatively poor overall fit to the ground motions, by all of the GMPE suites, at periods less than about 0.2 s and above 3 s, greater‐than‐predicted magnitude scaling for small to moderate‐magnitude events ( ⁠ M ≲ 5 "> M ≲ 5 ⁠ ), higher‐than‐predicted within‐event variability above 3 s, and an apparent geometric attenuation that is stronger than average predictions at close distances ( ⁠ R ≲ 20    km "> R ≲ 20 km ) and short periods ( ⁠ T ≲ 1 s "> T ≲ 1 s ). Our results indicate that regionally appropriate GMPEs for induced earthquakes should be used for predicting ground motions in Oklahoma and Kansas.

Kansas, Oklahoma↗
USGS2018

Updated California aftershock parameters

Reasenberg and Jones (1989) introduced a statistical model for aftershock rate following a mainshock along with estimates of “generic” California parameter values based on past aftershock sequences. The Reasenberg and Jones (1989) model has been used for decades to issue aftershock forecasts following M ≥ 5 "> M ≥ 5 mainshocks in California. Here, we update the “generic” parameters for California through a fit to the aftershock sequences of M ≥ 5 "> M ≥ 5 mainshocks occurring since 1980. We find aftershock productivity values that are lower on average than the generic productivity reported by Reasenberg and Jones (1989) , likely because low‐productivity sequences were omitted from their analysis and possibly because of a trade‐off between productivity and b "> b ‐value. We confirm the observation of Llenos and Michael (2017) that southern California sequences are more productive on average than northern California sequences. The Mendocino area is much less productive; the hydrothermal areas in Long Valley, Coso, and the Salton Sea, in contrast, are much more productive. We also quantify the variability of the Reasenberg and Jones (1989) productivity parameter a "> a a between sequences with a normal distribution. This distribution of a "> a ‐values can be used to compute aftershock forecasts that include epistemic uncertainty and can be used as the prior for Bayesian updating of the a "> a a ‐value as a sequence progresses.

California↗
USGS2019

The current unlikely earthquake hiatus at California’s transform boundary paleoseismic sites

Paleoseismic and historical earthquake records used to quantify earthquake recurrence rates can also be used to test the likelihood of seismically quiescent periods. At principal paleoseismic sites in California on the San Andreas, San Jacinto, Elsinore, and Hayward faults, no ground‐rupturing earthquake has occurred in the last 100 yr, yet this interval is about three times the average interearthquake period for the ensemble of sites. We examine long paleoseismic records from these faults, as they carry most of the transform fault slip on the plate boundary, to see if the current hiatus has any precedent in the last 1000 yr. The selection of sites is designed to sample fault sections unlikely to have ruptured together, so their conditional probabilities of a hiatus can be combined as independent events. We find a 100‐yr hiatus is not predicted by common time‐dependent or time‐independent recurrence models. Paleoearthquake dating uncertainties can allow long open intervals at individual sites or subsets of sites, but do not explain the observed gap in the ensemble. After approximately removing redundancies in the full paleoearthquake record, the time‐independent probability of the current 100‐yr gap is of order 0.3%. This raises several questions. Do we live in a statistically exceptional time? Or does some wide‐scale effect modulate earthquake occurrence among sites over longer timescales? Finally, how should we understand seismic hazard estimates in California if the recurrence models on which they rely seem, at minimum, incomplete? Whether due to a statistical anomaly, some longer‐term modulation of earthquake occurrence, or another cause, our results emphasize that the hiatus of the last century has been exceptional.

California↗
USGS2018

Do low-cost seismographs perform well enough for your network? An overview of laboratory tests and field observations of the OSOP Raspberry Shake 4D

Seismologists have recently begun utilizing low-cost nodal sensors in dense deployments to sample the seismic wavefield at unprecedented spatial resolution. Earthquake Early Warning Systems (EEWS) and other monitoring networks (e.g. wastewater injection) would additionally benefit from network densification; however, current nodal systems lack power systems and/or real-time data transmission required for these applications. A candidate sensor for these networks may instead be a low-cost, all-in-one package such as the OSOP Raspberry Shake 4D (RS-4D). The RS-4D includes a vertical component geophone, 3-component accelerometer, digitizer, and near real-time miniSEED data transmission, and costs only a few hundred dollars per unit. Here, we step through instrument testing of three RS-4Ds at the Albuquerque Seismological Laboratory. We find the geophones have sensitivities constrained to within 4% of nominal, but that they have relatively high self-noise levels compared to the broadband sensors typically used in seismic networks. To demonstrate the impact this would have on characterizing nearby events, we estimate local magnitudes of earthquakes in Oklahoma using Trillium Compact broadband sensor data from U.S. Geological Survey (USGS) aftershock deployments as well as 23 Raspberry Shakes operated by hobbyists and private owners within Oklahoma. We find that for ML 2.0-4.0 earthquakes at distances of 20-100 km from seismic stations, the Raspberry Shakes require events of magnitude ~0.3 larger than the broadband sensors in order to reliably estimate ML at a given distance from the epicenter. We conclude that RS-4Ds are suitable for densifying backbone networks designed for studies of local and regional events.

Seismological Research Letters↗
USGS2018

A collection of historic seismic instrumentation photographs at the Albuquerque Seismological Laboratory

The Albuquerque Seismological Laboratory (ASL) has preserved a collection of photographs of seismographic equipment, stations, and drawings used by the United States Coast and Geodetic Survey (USC&GS) in the early-to-mid-twentieth century. The photographs were transferred to ASL from the US Department of Commerce building in Washington DC after ASL became established as a USC&GS facility for seismological research and instrumentation testing in 1961. The photographs were variously used in publications to document USC&GS activities or used internally to document instrument installation, operation, and/or components. The historic photograph collection is made up of hundreds of photographs that were originally printed in the 1930s and 1940s. Our hope is that the archival of these records, as well as brief descriptions about their significance, will help preserve some of the knowledge about seismological advances in the United States during this time period. We provide digital scans of the complete ASL historic photo collection and discuss the historical context of select images in the Electronic Supplement of this document.

Seismological Research Letters↗
USGS2018

The Albuquerque Seismological Lab WWSSN film chip preservation project

From 1961 to 1996, the Albuquerque Seismological Laboratory (ASL) installed and operated the World‐Wide Standardized Seismograph Network (WWSSN). Each station within the network consisted of three Benioff short‐period sensors and three Sprengnether Press‐Ewing long‐period sensors along with recording, timing, and calibration equipment. Approximately 3.7 million single‐day record film chips were created from station records (paper seismograms) covering the period from 1962 to 1978. Two almost complete copies of these film chips are still known to exist at the ASL and at the Lamont–Doherty Earth Observatory (LDEO) as well as a couple of partial sets in other locations. To better preserve the data on these film chips, a project to scan the film chips and to make these scans available through the Incorporated Research Institutions for Seismology (IRIS) was started by W. H. K. Lee. The initial focus was on scanning film chips from a collection of specific earthquakes and nuclear events as well as complete scans of a number of reference stations. However, additional scans containing seismograms useful for climate studies were also completed. As part of this report, we cataloged all of the scanned WWSSN film chips with the hope that it serves as useful documentation as to what film chips have been scanned and of the location of the scans themselves at the IRIS‐Data Management Center (DMC) archive page (see Data and Resources ).

Seismological Research Letters↗
USGS2018

Seismology with dark data: Image-based processing of analog records using machine learning for the rangely earthquake control experiment

Before the digital era, seismograms were recorded in analog form and read manually by analysts. The digital era represents only about 25% of the total time span of instrumental seismology. Analog data provide important constraints on earthquake processes over the long term, and in some cases are the only data available. The media on which analog data are recorded degrades with time and there is an urgent need for cost‐effective approaches to preserve the information they contain. In this study, we work directly with images by constructing a set of image‐based methods for earthquake processing, rather than pursue the usual approach of converting analog data to vector time series. We demonstrate this approach on one month of continuous Develocorder films from the Rangely earthquake control experiment run by the U.S. Geological Survey (USGS). We scan the films into images and compress these into low‐dimensional feature vectors as input to a classifier that separates earthquakes from noise in a defined feature space. We feed the detected event images into a short‐term average/long‐term average (STA/LTA) picker, a grid‐search associator, and a 2D image correlator to measure both absolute arrival times and relative arrival‐time differences between events. We use these measurements to locate the earthquakes using hypoDD. In the month that we studied, we identified 40 events clustered near the injection wells. In the original study, Raleigh et al. (1976) identified only 32 events during the same period. Scanning without vectorizing analog seismograms represents an attractive approach to archiving these perishable data. We demonstrated that it is possible to carry out precision seismology directly on such images. Our approach has the potential for wide application to analog seismograms.

Seismological Research Letters↗
USGS2019

How physics‐based earthquake simulators might help improve earthquake forecasts

Questions have persisted on the usefulness of physics‐based earthquake simulators with respect to forecasting earthquakes, due mostly to the inevitable assumptions, approximations, and uncertainties. Whether any model is reliable or trustworthy depends entirely on what questions we are asking of it, so the point of this article is to outline a number of currently anticipated and desired inferences, informed largely by recent forecasting efforts in California. This article does not provide an in‐depth review of physics‐based simulators, nor does it render judgment on the usefulness question. The intent, rather, is to provide an explicit list of potential uses, or inferences, to enable more informed discussions among physics‐based modeling experts.

Seismological Research Letters↗
USGS2019

Rapid station and network quality analysis for temporary deployments

Seismic station data quality is commonly defined by metrics such as data completeness or background seismic noise levels in specific frequency bands. However, for temporary networks such as aftershock deployments or induced seismicity monitoring, the most critical metric is often how well the station performs when recording events of interest. A timely measure of station performance can be used for real-time network maintenance and to help make decisions about which stations may need to be moved or are redundant. We develop new event-based methods to assess station and network performance, including estimating network magnitude of completeness, determining station signal-to-noise ratios as a function of earthquake magnitude, and computing relative station amplitudes. At times, a complete catalog of local seismic events may not exist, such as in an aftershock deployment where hundreds to thousands of small earthquakes may be happening and catalog generation efforts cannot keep up. To overcome this, we use an envelope of the average energy recorded by the network to identify events of interest. We find that the log amplitude of events identified using this technique scales linearly with local earthquake magnitudes. This suggests that this approach can be used to determine seismicity rates and detection thresholds.

Seismological Research Letters↗
USGS2019

Site response in the Oklahoma region from seismic recordings of the 2011 Mw 5.7 Prague earthquake

We invert the shear-wave displacement spectra obtained from 30 three-component, broadband waveforms recorded within 300 km of the 6 November 2011 Mw 5.7 Prague, Oklahoma earthquake to recover the site-response contribution using an inversion method that simultaneously inverts for source, path, and site effects. Site-response functions identify resonant frequencies within a range of 0.1-10 Hz that generally coincide with spectral peaks in H/V curves derived from the recorded waveforms. S-wave velocity profiles available for several sites were also used to calculate theoretical SH transfer functions that predict the site amplification due to the near-surface soil structure down to depths of 30-50 m. These transfer functions are generally flat below about 8 Hz in the frequency range sampled by the spectral inversion process, indicating that the spectral peaks in the site response obtained from the waveform analysis result from deeper velocity variations. A 0.3-Hz spectral peak observed at several stations, for example, coincides with the strong, surface-wave amplitudes observed at 3s periods for induced M ≥ 3 earthquakes in Oklahoma and Kansas, suggesting that this resonant peak may be due to surface waves trapped in the upper sedimentary layer of the crust. Both shallow and deep contributions to the site response are important for the characterization of ground motion from Central and Eastern North America (CENA) earthquakes. We obtain a seismic moment of 4.32 × 1024 dyne-cm and a corner frequency of 0.229, consistent with the magnitude of the event. A frequency-dependent attenuation relation of Q(f)=1107f 0.398 consistent with prior measurements of path properties in CENA is also derived.

Oklahoma↗
USGS2019

Exotic Seismic Events Catalog (ESEC) Data Product

Nonearthquake seismic events from sources such as landslides, debris flows, dam collapses, floods, glaciers, and avalanches are rarely included in traditional earthquake catalogs. The new Incorporated Research Institutions for Seismology (IRIS) Data Management Center Exotic Seismic Events Catalog data product provides information on such events to help accelerate research in the area of environmental seismology. This catalog initially offers information on 113 events in four general categories consisting of flows, lahars, debris flows and outburst floods (17 events); rock or debris falls (23 events); rock, ice, or debris avalanches and slides (68 events); and snow avalanches (5 events). This database will be expanded as information regarding new recent and historical events becomes available. This catalog is now available to the research community at IRIS (see Data and Resources ).

Seismological Research Letters↗
USGS2019

Characterizing seismogenic fault structures in Oklahoma using a relocated template matched catalog

Oklahoma is one of the most seismically active places in the United States as a result of industry activities. In order to characterize the fault networks responsible for these earthquakes in Oklahoma, we relocated a large-scale template matching catalog between 2010-2016 using the GrowClust algorithm . This relocated catalog is currently the most complete statewide catalog for Oklahoma during this seven-year window. Using this relocated catalog, we identified seismogenic fault segments by developing an algorithm that clusters earthquakes and then identifies linear trends within each cluster. Considering the large number of earthquakes in Oklahoma, this algorithm made the process of identifying previously unmapped seismogenic faults more approachable and objective. We identify approximately 2500 seismogenic fault segments which are in general agreement with focal mechanisms and optimally oriented relative to maximum principle stress measurements. We demonstrate that these fault orientations can be used to approximate the maximum principle stress orientations.

Oklahoma↗
USGS2019

#EarthquakeAdvisory: Exploring discourse between government officials, news media and social media during the Bombay Beach 2016 Swarm

Communicating probabilities of natural hazards to varied audiences is a notoriously difficult task. Many of these challenges were encountered during the 2016 Bombay Beach, California, swarm of ~100 2≤M≤4.3 earthquakes, which began on 26 September 2016 and lasted for several days. The swarm’s proximity to the southern end of the San Andreas fault caused concern that a larger earthquake could be triggered. Within 1–2 days, different forecast models were used to evaluate the likelihood of a larger event with two agencies (the U.S. Geological Survey [USGS] and the California Governor’s Office of Emergency Services) releasing probabilities and forecasts for larger earthquakes. Our research explores communication and news media efforts, as well as how people on a microblogging social media site (Twitter) responded to these forecasts. Our findings suggest that news media used a combination of information sources, basing their articles on what they learned from social media, as well as using information provided by government agencies. As the swarm slowed down, there is evidence of the continued interplay between news media and social media, with the USGS issuing revised probability reports and scientists from the USGS and other institutions participating in media interviews. In reporting on the swarm, news media often used language more generally than the scientists; terms such as probability, likelihood, chance, and possibility were used interchangeably. Knowledge of how news media used scientific information from the 2016 Bombay Beach forecasts can assist local, state, and federal agencies in developing effective communication strategies to respond to future earthquakes.

California↗
USGS2019

Jack Boatwright’s last science

In the months before he passed away, Jack Boatwright asked us to review a manuscript on source properties, specifically stress drop, of earthquakes in northeastern North America (NENA). This manuscript originated in research funded by the U.S. Nuclear Regulatory Commission (NRC), described in his final report to NRC and published as USGS Open-File Report 2018-1073 (Boatwright, 2018). We wish to call attention to Boatwright (2018) for those who may not be aware of what Jack was unable to put into journal publications.

Seismological Research Letters↗