Rupture process of the M w7.9 Nepal earthquake April 25, 2015

A rapid, robust multiarray backprojection method was applied to image the rupture pattern of the 2015 Gorkha, Nepal Mw7.8 main shock and its Mw7.3 aftershock. Backprojected teleseismic P wave trains from three regional seismic arrays in Europe, Australia, and Alaska show that both earthquakes ruptured unilaterally and primarily eastward, with rupture speeds potentially decreasing with depth. The rupture of the main shock first extended ESEward at ∼3.5 km/s over ∼120 km, with later rupture propagation further downdip on the eastern segment at ∼2.1 km/s. The aftershock ruptured the fault SE of the main shock's ruptured plane. It began to rupture updipward for ∼20 km at a speed around 1.2 km/s, then it may have accelerated to 3.5 km/s for the next 50 km. The apparent depth‐dependent rupture speeds of the two earthquakes may be caused by along‐dip heterogeneities in fault strength, with a higher stress concentration on the updip part of the Nepalese Main Himalayan Thrust.

Section: Discussionsupporting

confidence: 62%

Section: Discussionmentioning

confidence: 99%

Multiarray rupture imaging of the devastating 2015 Gorkha, Nepal, earthquake sequence

Zhang

Lee

2016

“…Almost all aftershocks occurred to the southeast of the main shock. Few aftershocks occurred northeast of Kathmandu, where coseismic slip is large [ Avouac et al , ; Fan and Shearer , ; Lindsey et al , ; Wang et al , ; Wang and Fialko , ]. The M w 7.3 Kodari earthquake occurred on the eastern edge of the aftershock zone.…”

Section: Resultsmentioning

confidence: 99%

“…The study region showing the relocations of the M w 7.8 Gorkha, M w 7.3 Kodari earthquakes (yellow stars), aftershocks (red circles), and earthquakes that occurred before the Gorkha earthquake since 1980 (blue circles), which are superposed on a slip model [ Wang et al , ]. Historic seismicity of M w >7.0 since 1000 is shown with large black circles.…”

Section: Introductionmentioning

confidence: 99%

Faulting structure above the Main Himalayan Thrust as shown by relocated aftershocks of the 2015 M_w7.8 Gorkha, Nepal, earthquake

Bai

Liu

Ritsema

et al. 2016

The 25 April 2015, Mw7.8 Gorkha, Nepal, earthquake ruptured a shallow section of the Indian‐Eurasian plate boundary by reverse faulting with NNE‐SSW compression, consistent with the direction of current Indian‐Eurasian continental collision. The Gorkha main shock and aftershocks were recorded by permanent global and regional arrays and by a temporary local broadband array near the China‐Nepal border deployed prior to the Gorkha main shock. We relocate 272 earthquakes with Mw>3.5 by applying a multiscale double‐difference earthquake relocation technique to arrival times of direct and depth phases recorded globally and locally. We determine a well‐constrained depth of 18.5 km for the main shock hypocenter which places it on the Main Himalayan Thrust (MHT). Many of the aftershocks at shallower depths illuminate faulting structure in the hanging wall with dip angles that are steeper than the MHT. This system of thrust faults of the Lesser Himalaya may accommodate most of the elastic strain of the Himalayan orogeny.

“…The earthquake was well recorded by modern geodetic measurements [ Galetzka et al , ; Feng et al , ], providing us with an unprecedented opportunity to investigate the variations in dip. The overall fault dip is estimated to be approximately 6–11° based on seismic and geodetic analyses [ Avouac et al , ; Diao et al , ; Hayes et al , ; Liu and Ge , ; Shan et al , ; Wang and Fialko , ; Wang et al , ; Zhang and Xu , ; Zhang et al , ; Liu et al , ], suggesting that the earthquake mainly ruptured a flat portion of the MHT. Some geodetic analyses found that a listric fault could explain the surface deformations better than a planar fault could [ Wang and Fialko , ; Elliott et al , ], implying that ruptures may have reached the shallow steep fault branches.…”

Section: Introductionmentioning

confidence: 99%

Significant lateral dip changes may have limited the scale of the 2015 M_w 7.8 Gorkha earthquake

Yong

Wang

Walter

et al. 2017

The 2015 Mw 7.8 Gorkha earthquake has drawn interest due to its complex fault geometry. Both geodetic and geologic studies have focused on the dip variations. In this study we invert the coseismic geodetic data for the 2‐D dip variations of the earthquake. The best fit model confirms that the dip varies with depth, and suggests that there is a significant lateral dip anomaly along strike. The depth‐dependent dip variation suggests that the earthquake ruptured a ramp‐flat fault. The shallow ramp may have prevented the rupture breaking through the surface. In addition, a lateral large‐dip anomaly is found in the northeastern corner of the slip area, which supports the previous findings of inferred interseismic fault coupling, coseismic high‐frequency radiations, and the aftershock mechanisms. This lateral dip anomaly is likely associated with local tearing within the Indian slab. It may have blocked the east‐southeastward rupture propagations of the Gorkha earthquake, implying important controls on the earthquake scale and the spatial limits of ruptures.