The aftershock sequence of the 2015 April 25 Gorkha–Nepal earthquake

Adhikari, Lok Bijaya; Gautam, Umesh; Koirala, Bharat Prasad; Bhattarai, Madhusudan; Kandel, T.; Gupta, R.M.; Timsina, C.; Maharjan, N.; Maharjan, K.; Dahal, T.; Hoste-Colomer, Roser; Cano, Yoann; Dandine, M.; Guilhem, A.; Merrer, Sophie; Roudil, Pascal; Bollinger, Laurent

doi:10.1093/gji/ggv412

Cited by 115 publications

(65 citation statements)

References 20 publications

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“…This points to a lateral ramp on the MHT (Berger et al 2004) over which the rupture propagated eastwards. The SSW-NNE zone of aftershock concentration west of Katmandu (Adhikari et al 2015) possibly delineates the position of the lateral ramp, with transfer of stress in the overlying strata subsequent to rupture on a steeply dipping segment of the MHT ramp. The slip vectors for all the three subevents are consistently oriented to the S-SSW and results from overthrusting of the Himalayan wedge over the Indian Plate along the MHT.…”

Section: Discussionmentioning

confidence: 99%

“…Geodetic data combined with geologic, geomorphological and geophysical analysis (Elliott et al 2016) revealed that the main-shock slip occurred on the shallow flat portion of the MHT, between 5 and 15 km, and did not require any outof-sequence thrusting. Study of aftershock distribution (Adhikari et al 2015) highlighted three distinct southward extending belts of seismicity, reflecting possible regions of stress concentrations following the main-shock rupture.…”

Section: Introductionmentioning

confidence: 99%

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The 2015 April 25 Gorkha (Nepal) earthquake and its aftershocks: implications for lateral heterogeneity on the Main Himalayan Thrust

Kumar¹,

Singh²,

Mitra³

et al. 2016

Geophys. J. Int.

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S U M M A R YThe 2015 Gorkha earthquake (M w 7.8) occurred by thrust faulting on a ∼150 km long and ∼70 km wide, locked downdip segment of the Main Himalayan Thrust (MHT), causing the Himalaya to slip SSW over the Indian Plate, and was followed by major-to-moderate aftershocks. Back projection of teleseismic P-wave and inversion of teleseismic body waves provide constraints on the geometry and kinematics of the main-shock rupture and source mechanism of aftershocks. The main-shock initiated ∼80 km west of Katmandu, close to the locking line on the MHT and propagated eastwards along ∼117 • azimuth for a duration of ∼70 s, with varying rupture velocity on a heterogeneous fault surface. The main-shock has been modelled using four subevents, propagating from west-to-east. The first subevent (0-20 s) ruptured at a velocity of ∼3.5 km s −1 on a ∼6 • N dipping flat segment of the MHT with thrust motion. The second subevent (20-35 s) ruptured a ∼18 • W dipping lateral ramp on the MHT in oblique thrust motion. The rupture velocity dropped from 3.5 km s −1 to 2.5 km s −1 , as a result of updip propagation of the rupture. The third subevent (35-50 s) ruptured a ∼7 • N dipping, eastward flat segment of the MHT with thrust motion and resulted in the largest amplitude arrivals at teleseismic distances. The fourth subevent (50-70 s) occurred by left-lateral strikeslip motion on a steeply dipping transverse fault, at high angle to the MHT and arrested the eastward propagation of the main-shock rupture. Eastward stress build-up following the mainshock resulted in the largest aftershock (M w 7.3), which occurred on the MHT, immediately east of the main-shock rupture. Source mechanisms of moderate aftershocks reveal stress adjustment at the edges of the main-shock fault, flexural faulting on top of the downgoing Indian Plate and extensional faulting in the hanging wall of the MHT.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The 2015 April 25 Gorkha (Nepal) earthquake and its aftershocks: implications for lateral heterogeneity on the Main Himalayan Thrust

Kumar¹,

Singh²,

Mitra³

et al. 2016

Geophys. J. Int.

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“…With 121 grid points in latitude and 201 grid points in longitude we have approximately 3 km spacing laterally for hypocenter candidates. This grid definition was based upon calculations of aftershock locations carried out by Adhikari et al (2015) and Dixit et al (2015), and traveltimes for each phase were calculated a priori for every node in the grid using the LLNL-G3D 3-dimensional P-wave model of Simmons et al (2012).…”

Section: Case Study: the 2015 Gorkha Aftershock Sequence Nepalmentioning

confidence: 99%

Iterative Strategies for Aftershock Classification in Automatic Seismic Processing Pipelines

Gibbons

Kværna

Harris

et al. 2016

Seismological Research Letters

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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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“…Moment tensor solutions from telesiesmic data suggest that the Nepal earthquake occurred on a 10-20 dipping sub-horizontal blind thrust fault at about 15 km depth with a strike of 290 from the north 1 . The M w 7.8 event was followed by 553 aftershocks with magnitude >4, including two events having magnitudes 6.1 and 6.6 on the same day 4,5 . The largest aftershock occurred on 12 May 2015, about 150 km east of the main shock (Figure 1).…”

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confidence: 99%

“…Despite their global abundance 4 , the viral communities are still underexplored from any particular niche. Various microbial ecosystems such as soil associated ecosystem 5 , aquatic microbial ecosystem 6 and gut microbial community 7 have been studied for viruses using conventional methods.…”

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confidence: 99%

Constraints on Source Parameters of the 25 April 2015, M<sub>w</sub> = 7.8 Gorkha, Nepal Earthquake from Synthetic Aperture Radar Interferometry

Sreejith

Sunil²,

Ramesh³

et al. 2016

Current Science

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The aftershock sequence of the 2015 April 25 Gorkha–Nepal earthquake

Cited by 115 publications

References 20 publications

The 2015 April 25 Gorkha (Nepal) earthquake and its aftershocks: implications for lateral heterogeneity on the Main Himalayan Thrust

The 2015 April 25 Gorkha (Nepal) earthquake and its aftershocks: implications for lateral heterogeneity on the Main Himalayan Thrust

Iterative Strategies for Aftershock Classification in Automatic Seismic Processing Pipelines

Constraints on Source Parameters of the 25 April 2015, M<sub>w</sub> = 7.8 Gorkha, Nepal Earthquake from Synthetic Aperture Radar Interferometry

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