Rupture Passing Probabilities at Fault Bends and Steps, with Application to Rupture Length Probabilities for Earthquake Early Warning

Bulletin of the Seismological Society of America ◽

10.1785/0120200370 ◽

2021 ◽

Author(s):

Glenn P. Biasi ◽

Steven G. Wesnousky

Keyword(s):

Los Angeles ◽

Early Warning ◽

Earthquake Early Warning ◽

Fault System ◽

Bend Angle ◽

Earthquake Rupture ◽

Step Size ◽

Initiation Point ◽

Rupture Length ◽

Starting Point

ABSTRACT Earthquake early warning (EEW) systems can quickly identify the beginning of a significant earthquake rupture, but the first seconds of seismic data have not been found to predict the final rupture length. We present two approaches for estimating probabilities of rupture length given the rupture initiation from an EEW system. In the first approach, bends and steps on the fault are interpreted as physical mechanisms for rupture arrest. Arrest probability relations are developed from empirical observations and depend on bend angle and step size. Probability of arrest compounds serially with increasing rupture length as bends or steps are encountered. In the second approach, time-independent rates among ruptures from the Uniform California Earthquake Rupture Forecast, Version 3 (UCERF3), are interpreted to apply to the time-dependent condition in which rupture grows from a known starting point. Length probabilities from a Gutenberg–Richter magnitude–frequency relation provide a reference of comparison. We illustrate the new approach using the discretized fault model for California developed for UCERF3. For the case of rupture initiating on the southeast end of the San Andreas fault we find the geometric complexity of the Mill Creek section impedes most ruptures, and only ∼5% are predicted to reach to San Bernardino on the eastern edge of the greater Los Angeles region. Conditional probabilities of length can be precompiled in this manner for any initiation point on the fault system and thus are of potential value in seismic hazard and EEW applications.

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The “TRUAA” Seismic Network: Upgrading the Israel Seismic Network—Toward National Earthquake Early Warning System

Seismological Research Letters ◽

10.1785/0220200169 ◽

2020 ◽

Vol 91 (6) ◽

pp. 3236-3255 ◽

Cited By ~ 1

Author(s):

Ittai Kurzon ◽

Ran N. Nof ◽

Michael Laporte ◽

Hallel Lutzky ◽

Andrey Polozov ◽

...

Keyword(s):

Early Warning ◽

High Speed ◽

High Capacity ◽

Strong Motion ◽

Virtual Private Network ◽

Seismic Network ◽

Earthquake Early Warning ◽

Fault System ◽

Earthquake Early Warning System ◽

Private Network

Abstract Following the recommendations of an international committee (Allen et al., 2012), since October 2017, the Israeli Seismic Network has been undergoing significant upgrades, with 120 stations being added or upgraded throughout the country and the addition of two new datacenters. These enhancements are the backbone of the TRUAA project, assigned to the Geological Survey of Israel (GSI) by the Israeli Government, to provide earthquake early warning (EEW) capabilities for the state of Israel. The GSI contracted Nanometrics (NMX), supported by Motorola Solutions Israel, to deliver these upgrades through a turnkey project, including detailed design, equipment supply, and deployment of the network and two datacenters. The TRUAA network was designed and tailored by the GSI, in collaboration with the NMX project team, specifically to achieve efficient and robust EEW. Several significant features comprise the pillars of this network:Coverage: Station distribution has high density (5–10 km spacing) along the two main fault systems—the Dead Sea Fault and the Carmel Fault System;Instrumentation: High-quality strong-motion accelerometers and broadband seismometers with modern three-channel and six-channel dataloggers sampling at 200 samples per second;Low latency acquisition: Data are encapsulated in small packets (<1 s), with primary routing via high-speed, high-capacity telemetry links (<1 s latency);Robustness: High level of redundancy throughout the system design:Dual active-active redundant acquisition routes from each station, each utilizing multicast streaming over an IP security Virtual Private Network tunnel, via independent high-bandwidth telemetry systemsTwo active-active independent geographically separate datacentersDual active-active redundant independent automatic seismic processing tool chains within each datacenter, implemented in a high availability protected virtual environment. At this time, both datacenters and over 100 stations are operational. The system is currently being commissioned, with initial early warning operation targeted for early 2021.

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Event Detection Performance of the PLUM Earthquake Early Warning Algorithm in Southern California

Bulletin of the Seismological Society of America ◽

10.1785/0120180326 ◽

2019 ◽

Vol 109 (4) ◽

pp. 1524-1541 ◽

Cited By ~ 6

Author(s):

Elizabeth S. Cochran ◽

Julian Bunn ◽

Sarah E. Minson ◽

Annemarie S. Baltay ◽

Deborah L. Kilb ◽

...

Keyword(s):

Los Angeles ◽

Ground Motion ◽

Early Warning ◽

Southern California ◽

Ground Motions ◽

Tohoku Earthquake ◽

Prediction Equation ◽

Earthquake Early Warning ◽

Japan Meteorological Agency ◽

Origin Time

Abstract We test the Japanese ground‐motion‐based earthquake early warning (EEW) algorithm, propagation of local undamped motion (PLUM), in southern California with application to the U.S. ShakeAlert system. In late 2018, ShakeAlert began limited public alerting in Los Angeles to areas of expected modified Mercalli intensity (IMMI) 4.0+ for magnitude 5.0+ earthquakes. Most EEW systems, including ShakeAlert, use source‐based methods: they estimate the location, magnitude, and origin time of an earthquake from P waves and use a ground‐motion prediction equation to identify regions of expected strong shaking. The PLUM algorithm uses observed ground motions directly to define alert areas and was developed to address deficiencies in the Japan Meteorological Agency source‐based EEW system during the 2011 Mw 9.0 Tohoku earthquake sequence. We assess PLUM using (a) a dataset of 193 magnitude 3.5+ earthquakes that occurred in southern California between 2012 and 2017 and (b) the ShakeAlert testing and certification suite of 49 earthquakes and other seismic signals. The latter suite includes events that challenge the current ShakeAlert algorithms. We provide a first‐order performance assessment using event‐based metrics similar to those used by ShakeAlert. We find that PLUM can be configured to successfully issue alerts using IMMI trigger thresholds that are lower than those implemented in Japan. Using two stations, a trigger threshold of IMMI 4.0 for the first station and a threshold of IMMI 2.5 for the second station PLUM successfully detect 12 of 13 magnitude 5.0+ earthquakes and issue no false alerts. PLUM alert latencies were similar to and in some cases faster than source‐based algorithms, reducing area that receives no warning near the source that generally have the highest ground motions. PLUM is a simple, independent seismic method that may complement existing source‐based algorithms in EEW systems, including the ShakeAlert system, even when alerting to light (IMMI 4.0) or higher ground‐motion levels.

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Earthquake rupture characteristics along a developing transform boundary

Geophysical Journal International ◽

10.1093/gji/ggz357 ◽

2019 ◽

Vol 219 (2) ◽

pp. 1237-1252

Author(s):

J S Neely ◽

Y Huang ◽

W Fan

Keyword(s):

Stress Drop ◽

Spectral Ratio ◽

Fault System ◽

Corner Frequency ◽

Ratio Method ◽

Earthquake Rupture ◽

Independent Evidence ◽

Rupture Length ◽

Spectral Models ◽

Transform Boundary

SUMMARY The 280-km-long San Cristobal Trough (SCT), created by the tearing of the Australia plate as it subducts under the Pacific Plate near the Solomon and Vanuatu subduction zones, has hosted strike-slip earthquake sequences in 1993 and 2015. Both sequences, which likely represent a complete seismic cycle, began along the oldest section of the SCT—the portion farthest from the tear that has experienced the most cumulative displacement—and migrated to the younger sections closer to the tear. The SCT's abundant seismicity allows us to study transform boundary development—a process rarely observed along a single fault system—through observations of earthquake rupture properties. Using the spectral ratio method based on empirical Green's functions (EGFs), we calculate the corner frequencies of three Mw ∼7 2015 earthquakes and colocated smaller earthquakes. We utilize two different spectral ratio stacking methods and fit both Brune and Boatwright models to the stacked spectral ratios. Regardless of stacking methods and spectral models, we find that the corner frequencies of the 2015 Mw ∼7 earthquakes decrease slightly with distance from the tear. Assuming a constant rupture velocity and an omega-square spectral model, this corner frequency decrease may be due to an increase in rupture length with distance from the tear. The spectrum of the 2015 earthquake farthest from the tear also deviates from the omega-square model, which may indicate rupture complexity. Stress drop estimates from the corner frequencies of the 2015 Mw ∼7 earthquakes range between 1 and 7 MPa, whereas stress drop estimates of their EGFs range from ∼0.05 to 10 MPa with most values between 0.1 and 1 MPa. Independent evidence from a second moments analysis of the 2015 earthquake sequence also indicates a possible increase in rupture length with distance from the tear, confirming the results from the spectral ratio analysis. We also observe an increase in normalized centroid time-delay values, a first-order proxy for rupture behaviour, with distance from the tear for the 2015 sequence. A similar trend for the 1993 sequence suggests that earthquake rupture varies systematically along the SCT. Since distance from the tear corresponds to cumulative fault displacement, these along-strike rupture variations may be due to a displacement-driven fault maturation process.

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CyberShake-derived ground-motion prediction models for the Los Angeles region with application to earthquake early warning

Geophysical Journal International ◽

10.1093/gji/ggu198 ◽

2014 ◽

Vol 198 (3) ◽

pp. 1438-1457 ◽

Cited By ~ 2

Author(s):

Maren Böse ◽

Robert W. Graves ◽

David Gill ◽

Scott Callaghan ◽

Philip J. Maechling

Keyword(s):

Los Angeles ◽

Ground Motion ◽

Early Warning ◽

Prediction Models ◽

Earthquake Early Warning ◽

Motion Prediction ◽

Ground Motion Prediction

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More Fault Connectivity Is Needed in Seismic Hazard Analysis

Bulletin of the Seismological Society of America ◽

10.1785/0120200119 ◽

2020 ◽

Author(s):

Morgan T. Page

Keyword(s):

San Andreas Fault ◽

Hazard Analysis ◽

Length Distribution ◽

Fault System ◽

Earthquake Rupture ◽

Present Evidence ◽

The Third ◽

Rupture Length ◽

San Andreas ◽

Improve Model

ABSTRACT Did the third Uniform California Earthquake Rupture Forecast (UCERF3) go overboard with multifault ruptures? Schwartz (2018) argues that there are too many long ruptures in the model. Here, I address his concern and show that the UCERF3 rupture-length distribution matches empirical data. I also present evidence that, if anything, the UCERF3 model could be improved by adding more connectivity to the fault system. Adding more connectivity would improve model misfits with data, particularly with paleoseismic data on the southern San Andreas fault; make the model less characteristic on the faults; potentially improve aftershock forecasts; and reduce model sensitivity to inadequacies and unknowns in the modeled fault system.

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ShakeAlert Earthquake Early Warning System Performance during the 2019 Ridgecrest Earthquake Sequence

Bulletin of the Seismological Society of America ◽

10.1785/0120200032 ◽

2020 ◽

Vol 110 (4) ◽

pp. 1904-1923 ◽

Cited By ~ 3

Author(s):

Angela I. Chung ◽

Men-Andrin Meier ◽

Jennifer Andrews ◽

Maren Böse ◽

Brendan W. Crowell ◽

...

Keyword(s):

Los Angeles ◽

Early Warning ◽

Early Warning System ◽

Los Angeles County ◽

Warning System ◽

Earthquake Early Warning ◽

Earthquake Early Warning System ◽

Sequence Of Events ◽

Finite Fault ◽

The U.S

ABSTRACT During July 2019, a sequence of earthquakes, including an Mw 6.4 foreshock and an Mw 7.1 mainshock, occurred near Ridgecrest, California. ShakeAlert, the U.S. Geological Survey (USGS) earthquake early warning system being developed for the U.S. West Coast, was operational during this time, although public alerting was only available within Los Angeles County. ShakeAlert created alert messages for the two largest events and for many of the larger aftershocks. In this study, we dissect log files and replay data through the system to reconstruct the sequence of events and analyze the performance of the system during that period. Although the system performed reasonably well overall, the sequence also revealed various issues and short comings that will be addressed in impending and future system upgrades. ShakeAlert detected and characterized both the Mw 6.4 and Mw 7.1 earthquakes within 6.9 s of their origin times and created alert messages that were available to ShakeAlert’s pilot users. No public alerts were sent out by the ShakeAlertLA cell phone app (the only publicly available alerting method at the time), because the predicted shaking for Los Angeles County was below the app’s alerting threshold of modified Mercalli intensity 4.0. For the Mw 6.4 event, this was accurate. For the Mw 7.1 event, public alerts for Los Angeles County were warranted, but ShakeAlert underpredicted the shaking levels, because both the point-source and finite-fault algorithms underestimated the magnitude of the earthquake by 0.8 units. A number of software and hardware issues that were responsible for the magnitude underestimation of the mainshock have been identified and will be addressed in future ShakeAlert releases. We also analyze the hypothetical alerting performance of ShakeAlert had public alerting been available throughout southern California.

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