Rapid Characterization of the 2015<i>M</i><sub>w</sub> 7.8 Gorkha, Nepal, Earthquake Sequence and Its Seismotectonic Context

Aftershock sequences following very large earthquakes present enormous challenges to nearrealtime generation of seismic bulletins. The increase in analyst resources needed to relocate an inflated number of events is compounded by failures of phase association algorithms and a significant deterioration in the quality of underlying fully automatic event bulletins. Current processing pipelines were designed a generation ago and, due to computational limitations of the time, are usually limited to single passes over the raw data. With current processing capability, multiple passes over the data are feasible. Processing the raw data at each station currently generates parametric datastreams which are then scanned by a phase association algorithm to form event hypotheses. We consider the scenario where a large earthquake has occurred and propose to define a region of likely aftershock activity in which events are detected and accurately located using a separate specially targeted semi-automatic process. This effort may focus on so-called pattern detectors, but here we demonstrate a more general grid search algorithm which may cover wider source regions without requiring waveform similarity. Given many well-located aftershocks within our source region, we may remove all associated phases from the original detection lists prior to a new iteration of the phase association algorithm. We provide a proof-of-concept example for the 2015 Gorkha sequence, Nepal, recorded on seismic arrays of the International Monitoring System. Even with very conservative conditions for defining event hypotheses within the aftershock source region, we can automatically remove about half of the original detections which could have been generated by Nepal earthquakes and reduce the likelihood of false associations and spurious event

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“…The spatial distribution of these event hypotheses is very similar to that obtained from manual relocations (e.g. Hayes et al, 2015). …”

Section: Case Study: the 2015 Gorkha Aftershock Sequence Nepalsupporting

confidence: 71%

Iterative Strategies for Aftershock Classification in Automatic Seismic Processing Pipelines

Gibbons

Kværna

Harris

et al. 2016

Seismological Research Letters

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“…The difference between their and our resulting slip distribution is that over 4 m slip area expanded to about 50 km east of Kathmandu is only seen in Grandin et al (2015). This slip can be observed in other studies that used InSAR data (Feng et al 2015;Galetzka et al 2015;Hayes et al 2015;Kobayashi et al 2015;Lindsey et al 2015;Wang and Fialko 2015); however, Avouac et al (2015) also used InSAR data, and their resulting slip distribution does not show the slip in question. This is probably because one of the two InSAR images used by Avouac et al (2015) does not cover the eastern region of Kathmandu.…”

Section: Joint Source Inversionmentioning

confidence: 39%

“…Therefore, an investigation of the rupture process of the Gorkha earthquake is crucial to explore potential reasons underlying these peculiar features. Previous source studies of the Gorkha earthquake were performed using teleseismic waveforms (Fan and Shearer 2015;Yagi and Okuwaki 2015); InSAR (Kobayashi et al 2015;Lindsey et al 2015); teleseismic waveforms and InSAR Hayes et al 2015); static GPS and InSAR (Feng et al 2015;Wang and Fialko 2015); static GPS, highrate GPS, and InSAR (Galetzka et al 2015); teleseismic Open Access *Correspondence: khiro@eri.u-tokyo.ac.jp 1 Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, Japan Full list of author information is available at the end of the article waveforms, strong motion, static GPS, high-rate GPS, and InSAR (Grandin et al 2015); and teleseismic waveforms, static GPS, and high-rate GPS (Kubo et al 2016). Near-field waveforms are most effective to investigate the spatiotemporal earthquake rupture process.…”

Section: Introductionmentioning

confidence: 99%

Joint inversion of teleseismic, geodetic, and near-field waveform datasets for rupture process of the 2015 Gorkha, Nepal, earthquake

Kobayashi

Koketsu

Takai

et al. 2016

Earth Planets Space

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The 2015 Gorkha earthquake and its aftershocks caused severe damage mostly in Nepal, while countries around the Himalayan region were warned for decades about large Himalayan earthquakes and the seismic vulnerability of these countries. However, the magnitude of the Gorkha earthquake was smaller than those of historical earthquakes in Nepal, and the most severe damage occurred in the north and northeast of Kathmandu. We explore reasons for these unexpected features by performing a joint source inversion of teleseismic, geodetic, and near-field waveform datasets to investigate the rupture process. Results indicate that the source fault was limited to the northern part of central Nepal and did not reach the Main Frontal Thrust. The zone of large slip was located in the north of Kathmandu, and the fault rupture propagated eastward with an almost constant velocity. Changes in the Coulomb failure function (ΔCFF) due to the Gorkha earthquake were computed, indicating that southern and western regions neighboring the source fault are potential source regions for future earthquakes related to the Gorkha earthquake. These two regions may correspond to the historical earthquakes of 1866 and 1344. Possible future earthquakes in the regions are predicted, and the warning for Himalayan seismic hazards remains high even after the Gorkha earthquake.

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“…Several efforts have been made in the Central Nepal region that was struck by large earthquakes like 1833, 1934 AD and the recent 2015 Gorkha earthquake to estimate the surface ruptures and constrain the timing of last and penultimate events (Bilham 1995;Campbell 1833a, b;Dunn et al 1939;Hayes et al 2015). Clear evidence of the surface deformation along the river-cut cliff in the east of Mahara River and presence of six levels of terraces along Bardibas and Patu Thrust suggested coseismic uplift (Sapkota et al 2013).…”

Section: Central Nepalmentioning

confidence: 99%

Overestimation of the earthquake hazard along the Himalaya: constraints in bracketing of medieval earthquakes from paleoseismic studies

Arora

Malik

2017

Geosci. Lett.

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The Himalaya is one of the most seismically active regions of the world. (Mw 7.8) are the testimony to ongoing tectonic activity. In the last few decades, tremendous efforts have been made along the Himalayan arc to understand the patterns of earthquake occurrences, size, extent, and return periods. Some of the large magnitude earthquakes produced surface rupture, while some remained blind. Furthermore, due to the incompleteness of the earthquake catalogue, a very few events can be correlated with medieval earthquakes. Based on the existing paleoseismic data certainly, there exists a complexity to precisely determine the extent of surface rupture of these earthquakes and also for those events, which occurred during historic times. In this paper, we have compiled the paleo-seismological data and recalibrated the radiocarbon ages from the trenches excavated by previous workers along the entire Himalaya and compared earthquake scenario with the past. Our studies suggest that there were multiple earthquake events with overlapping surface ruptures in small patches with an average rupture length of ~300 km limiting Mw 7.8-8.0 for the Himalayan arc, rather than two or three giant earthquakes rupturing the whole front. It has been identified that the large magnitude Himalayan earthquakes, such as 1905 Kangra, 1934 Bihar-Nepal, and 1950 Assam, that have occurred within a time frame of 45 years. Now, if these events are dated, there is a high possibility that within the range of ±50 years, they may be considered as the remnant of one giant earthquake rupturing the entire Himalayan arc. Therefore, leading to an overestimation of seismic hazard scenario in Himalaya.

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Rapid Characterization of the 2015M_w 7.8 Gorkha, Nepal, Earthquake Sequence and Its Seismotectonic Context

Cited by 91 publications

References 39 publications

Iterative Strategies for Aftershock Classification in Automatic Seismic Processing Pipelines

Iterative Strategies for Aftershock Classification in Automatic Seismic Processing Pipelines

Joint inversion of teleseismic, geodetic, and near-field waveform datasets for rupture process of the 2015 Gorkha, Nepal, earthquake

Overestimation of the earthquake hazard along the Himalaya: constraints in bracketing of medieval earthquakes from paleoseismic studies

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Rapid Characterization of the 2015Mw 7.8 Gorkha, Nepal, Earthquake Sequence and Its Seismotectonic Context

Cited by 91 publications

References 39 publications

Iterative Strategies for Aftershock Classification in Automatic Seismic Processing Pipelines

Iterative Strategies for Aftershock Classification in Automatic Seismic Processing Pipelines

Joint inversion of teleseismic, geodetic, and near-field waveform datasets for rupture process of the 2015 Gorkha, Nepal, earthquake

Overestimation of the earthquake hazard along the Himalaya: constraints in bracketing of medieval earthquakes from paleoseismic studies

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Rapid Characterization of the 2015M_w 7.8 Gorkha, Nepal, Earthquake Sequence and Its Seismotectonic Context