Efforts toward automatic aftershock sequences processing at the International Data Centre

2021 ◽  
Author(s):  
Christos Saragiotis
Keyword(s):  
Main Shock ◽  
Tohoku Earthquake ◽  
Seismic Events ◽  
Gorkha Earthquake ◽  
Strong Earthquakes ◽  
Aftershock Sequences ◽  
Order Of Magnitude ◽  
International Data ◽  
Nuclear Tests ◽  
Illapel Earthquake

<div> <p>The number of aftershocks after a large main shock may increase the daily number of seismic events by an order of magnitude for a few days or even weeks. The large number of incoming arrivals reduces the effectiveness of automatic bulletin generation and significantly increases the work of the analysts. In the verification context such aftershocks may delay the production of the CTBTO Reviewed Event Bulletin, as well as mask clandestine nuclear tests. Consequently, the CTBTO has been investigating ways to improve the performance of the automatic processing during aftershock sequences.  </p> </div><div> <p>In line with this investigation, the PTS launched a project with the objective to evaluate three algorithms that could address this issue, namely the Empirical Matched Field developed at NORSAR, the SeisCorr developed at Sandia National Labs and XSEL developed at the IDC. In this abstract we present comparisons on the performance of the three methods on the aftershock sequences of four very strong earthquakes: the Tohoku earthquake in Japan (March 2011), the Gorkha earthquake in Nepal (April 2015), the  Illapel earthquake off the coast of Chile (September 2015) and the devastating earthquake in Papua New Guinea (February 2018).</p> </div>

Applying Waveform Correlation to Reduce Seismic Analyst Workload Due to Repeating Mining Blasts

2021 ◽  
Author(s):  
Amy Sundermier ◽  
Rigobert Tibi ◽  
Ronald A. Brogan ◽  
Christopher J. Young
Keyword(s):  
Global Network ◽  
Seismic Events ◽  
Selection Threshold ◽  
International Monitoring ◽  
Correlation Processing ◽  
International Data ◽  
Template Selection ◽  
Nuclear Tests ◽  
Threshold Setting ◽  
Test Ban

ABSTRACT Agencies that monitor for underground nuclear tests are interested in techniques that automatically characterize mining blasts to reduce the human analyst effort required to produce high-quality event bulletins. Waveform correlation is effective in finding similar waveforms from repeating seismic events, including mining blasts. We report the results of an experiment to detect and identify mining blasts for two regions, Wyoming (U.S.A.) and Scandinavia, using waveform templates recorded by multiple International Monitoring System stations of the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO PrepCom) for up to 10 yr prior to the time of interest. We discuss approaches for template selection, threshold setting, and event detection that are specialized for characterizing mining blasts using a sparse, global network. We apply the approaches to one week of data for each of the two regions to evaluate the potential for establishing a set of standards for waveform correlation processing of mining blasts that can be generally applied to operational monitoring systems with a sparse network. We compare candidate events detected with our processing methods to the Reviewed Event Bulletin of the International Data Centre to assess potential reduction in analyst workload.

scholarly journals Seismic Damage Accumulation in Highway Bridges in Earthquake-Prone Regions

2015 ◽  
Vol 31 (1) ◽  
pp. 115-135 ◽  
Author(s):  
Jayadipta Ghosh ◽  
Jamie E. Padgett ◽  
Mauricio Sánchez-Silva
Keyword(s):  
Service Life ◽  
Damage Accumulation ◽  
Main Shock ◽  
Prediction Models ◽  
Time Window ◽  
Damage Index ◽  
Active Regions ◽  
Highway Bridges ◽  
Main Shocks ◽  
Aftershock Sequences

Civil infrastructures, such as highway bridges, located in seismically active regions are often subjected to multiple earthquakes, including multiple main shocks during their service life or main shock–aftershock sequences. Repeated seismic events result in reduced structural capacity and may lead to bridge collapse, causing disruption in the normal functioning of transportation networks. This study proposes a framework to predict damage accumulation in structures subjected to multiple shock scenarios after developing damage index prediction models and accounting for the probabilistic nature of the hazard. The versatility of the proposed framework is demonstrated on a case-study highway bridge located in California for two distinct hazard scenarios: (1) multiple main shocks during the service life and (2) multiple aftershock earthquake occurrences following a single main shock. Results reveal that in both cases there is a significant increase in damage index exceedance probabilities due to repeated shocks within the time window of interest.

scholarly journals LEAST SQUARE SUPPORT VECTOR MACHINE FOR DETECTION OF TECSEISMO- IONOSPHERIC ANOMALIES ASSOCIATED WITH THE POWERFUL NEPAL EARTHQUAKE (M<sub>w</sub> = 7.5) OF 25 APRIL 2015

2016 ◽  
Vol III-8 ◽  
pp. 3-11
Author(s):  
M. Akhoondzadeh
Keyword(s):  
Support Vector Machine ◽  
Main Shock ◽  
Warning System ◽  
Least Square ◽  
Support Vector ◽  
Electron Content ◽  
Total Electron ◽  
Strong Earthquakes ◽  
Nepal Earthquake ◽  
New Challenges

Due to the irrepalable devastations of strong earthquakes, accurate anomaly detection in time series of different precursors for creating a trustworthy early warning system has brought new challenges. In this paper the predictability of Least Square Support Vector Machine (LSSVM) has been investigated by forecasting the GPS-TEC (Total Electron Content) variations around the time and location of Nepal earthquake. In 77 km NW of Kathmandu in Nepal (28.147° N, 84.708° E, depth&thinsp;=&thinsp;15.0 km) a powerful earthquake of M&lt;sub&gt;w&lt;/sub&gt;&thinsp;=&thinsp;7.8 took place at 06:11:26 UTC on April 25, 2015. For comparing purpose, other two methods including Median and ANN (Artificial Neural Network) have been implemented. All implemented algorithms indicate on striking TEC anomalies 2 days prior to the main shock. Results reveal that LSSVM method is promising for TEC sesimo-ionospheric anomalies detection.

scholarly journals Seismic observations of crevasse growth following rain-induced glacier acceleration, Haupapa/Tasman Glacier, New Zealand

2019 ◽  
Vol 60 (79) ◽  
pp. 14-22
Author(s):  
Samuel Taylor-Offord ◽  
Huw Horgan ◽  
John Townend ◽  
J. Paul Winberry
Keyword(s):  
New Zealand ◽  
Strain Rate ◽  
Rain Rate ◽  
Ice Sheets ◽  
Seismic Events ◽  
Seismicity Rate ◽  
Acceleration Rate ◽  
Order Of Magnitude ◽  
Strain Rate Field ◽  
Magnitude Increase

ABSTRACTChanging rates of water input can affect both the flow of glaciers and ice sheets and their propensity to crevasse. Here we examine geodetic and seismic observations during two substantial (10–18-times background velocity) rain-induced glacier accelerations at Haupapa/Tasman Glacier, New Zealand. Changes in rain rate result in glacier acceleration and associated uplift, which propagate down-glacier. This pattern of acceleration results in a change to the strain rate field, which correlates with an order of magnitude increase in the apparent seismicity rate and an overall down-glacier migration in located seismicity. After each acceleration event the apparent seismicity rate decreases to below the pre-acceleration rate for 3 days. This suggests that seismic events associated with surface crevasse growth occur early during phases of glacier acceleration due to elevated extensional stresses, and then do not occur again until stresses recover.

Seismotectonics of the northern Longitudinal Valley, Taiwan, inferred from aftershock sequences of 2018 Mw6.4 and 2019 Mw6.2 Hualien earthquakes

2020 ◽  
Author(s):  
Wei-Fang Sun ◽  
Hao Kuo-Chen ◽  
Zhuo-Kang Guan ◽  
Wen-Yen Chang
Keyword(s):  
Main Shock ◽  
Surface Deformation ◽  
Plate Boundary ◽  
Aftershock Sequence ◽  
Tectonic Structures ◽  
Seismicity Rate ◽  
Transitional Area ◽  
Main Shocks ◽  
Aftershock Sequences ◽  
Seismic Networks

&lt;p&gt;In the Hualien area, two Mw6.4 and Mw6.2 earthquakes, 20 km apart, occurred in February 2018 and April 2019 respectively. The former to the northeast, located offshore to &amp;#8203;&amp;#8203;the Liwu river, triggered several earthquake clusters along the Milun fault and southward to the Longitudinal Valley, the suture of the Eurasian and the Philippine Sea plates; the latter to the southwest, located in the Central Range, also triggered several seismic swarms in the Central Range, &amp;#160;along the Liwu river to the northeast and at Ji'an to the southeast. Except for the Milun fault, neither GPS nor InSAR observations detects significant surface deformation after the occurrence of these two main shocks, indicating that the earthquake ruptures mainly developed within the crust. Therefore, seismic observation becomes an efficient tool for revealing the seismotectonics of the two earthquake sequences. For monitoring the aftershock sequences, two days after the main shocks, we deployed two geophone arrays, 70 Z-component RefTek 125A TEXANs for two weeks in 2018 and 47 three-component Fairfield Nodal Z-Lands for one month in 2019, with 1-5 km station spacing around the Hualien City. These earthquake swarms were well recorded and analyzed through the dense seismic networks. The numbers of aftershock sequences manually identified are two-fold more than that issued by the Central Weather Bureau, Taiwan. The seismicity of the 2018 aftershock sequence, to depths of between 5-15 km, was significantly reduced within 10 days after the main shock. however, the seismicity of the 2019 aftershock sequence, to depths of between 2-50 km, was still above background seismicity rate 30 days after the main shock. The spatial distribution of the 2018 aftershock sequence could be related to a fault zone of the plate boundary, but that of the 2019 and the relocated 1986 aftershock sequences show a conjugate thrust fault pair beneath the eastern Central Range. Our results clearly depict several local tectonic structures that have not been observed at the northern tip of the Longitudinal Valley, not only a suture but also a transitional area from collision to subduction.&lt;/p&gt;

Characterizing Aftershock Sequences of the Recent Strong Earthquakes in Central Italy

2017 ◽  
Vol 174 (10) ◽  
pp. 3713-3723 ◽  
Author(s):  
Vladimir G. Kossobokov ◽  
Anastasia K. Nekrasova
Keyword(s):  
Central Italy ◽  
Strong Earthquakes ◽  
Aftershock Sequences

Responses of Two Tall Buildings in Tokyo, Japan, before, during, and after the M9.0 Tohoku Earthquake of 11 March 2011

2016 ◽  
Vol 32 (1) ◽  
pp. 463-495 ◽  
Author(s):  
Mehmet Çelebi ◽  
Yoshiaki Hisada ◽  
Roshanak Omrani ◽  
S. Farid Ghahari ◽  
Ertugrul Taciroglu
Keyword(s):  
Urban Areas ◽  
Main Shock ◽  
Nonlinear Behavior ◽  
Tall Buildings ◽  
Tohoku Earthquake ◽  
Ground Level ◽  
The United States ◽  
Time Interval ◽  
Long Period ◽  
Fundamental Frequencies

The 11 March 2011 M 9.0 Tohoku earthquake generated significant long duration shaking that propagated hundreds of kilometers from the epicenter and affected urban areas throughout much of Honshu. Recorded responses of tall buildings at several hundred km from the epicenter of the main shock and other events show tall buildings were affected by long-period motions of events at distant sources. This study presents behavioral aspects of 29-story and 30-story neighboring buildings in the Shinjuku area of Tokyo, Japan, as inferred from records retrieved from a sparse array of accelerometers deployed in the superstructures, at ground and 100 m below the ground level over a time interval covering before, during, and after the main shock. Such long-period effects are common in several regions of Japan as well as in the United States and in other seismically active countries. Permanent shifts in fundamental frequencies are observed. Drift ratios indicate possible structural nonlinear behavior occurred during the main shock. The need to consider risks to built environments from distant sources, including those in neighboring countries, is emphasized.

scholarly journals A project of creating atlas aftershocks of strong earthquakes

2019 ◽  
pp. 79-84
Author(s):  
A. V. Guglielmi ◽  
A. D. Zavyalov ◽  
O. D. Zotov
Keyword(s):  
Inverse Problem ◽  
Strong Earthquake ◽  
Main Shock ◽  
Earthquake Source ◽  
Problem Solution ◽  
Strong Earthquakes ◽  
Omori Law ◽  
The Earth ◽  
Interesting Possibility ◽  
Source Physics

The Omori Law, which describes the repeated underground shocks after a strong earthquake, is written in the form of a nonlinear differential equation. An idea of the focal deactivation coefficient after the main shock is introduced. Two advantages of the new wording of the Omori Law are given. Firstly, there is an interesting possibility to naturally take into account exogenous and endogenous triggers affecting the earthquake source. Endogenous triggers in the form of round-the-world seismic echo and free oscillations of the Earth, excited by the main shock, are especially noted. The second advantage is that the differential aftershock equation makes it possible to put the reverse problem of the earthquake source physics. The essence of the inverse problem is to determine the deactivation coefficient from the data on the observed aftershock frequency. Examples of inverse problem solution are given. The project of creation of the Atlas of aftershocks on the basis of the solution of the inverse problem of the source, cooling down after a strong earthquake is offered.

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