Seismotectonics of the April–May 2015 Nepal earthquakes: An assessment based on the aftershock patterns, surface effects and deformational characteristics

Occurrence of the April 25, 2015 (Mw 7.8) earthquake near Gorkha, central Nepal, and another one that followed on May 12 (Mw 7.3), located similar to 140 km to its east, provides an exceptional opportunity to understand some new facets of Himalayan earthquakes. Here we attempt to assess the seismotectonics of these earthquakes based on the deformational field generated by these events, along with the spatial and temporal characteristics of their aftershocks. When integrated with some of the post-earthquake field observations, including the localization of damage and surface deformation, it became obvious that although the mainshock slip was mostly limited to the Main Himalayan Thrust (MHT), the rupture did not propagate to the Main Frontal Thrust (MFT). Field evidence, supported by the available InSAR imagery of the deformation field, suggests that a component of slip could have emerged through a previously identified out-of-sequence thrust/active thrust in the region that parallels the Main Central Thrust (MCT), known in the literature as a co-linear physiographic transitional zone called PT2. Termination of the first rupture, triggering of the second large earthquake, and distribution of aftershocks are also spatially constrained by the eastern extremity of PT2. Mechanism of the 2015 sequence demonstrates that the out-of-sequence thrusts may accommodate part of the slip, an aspect that needs to be considered in the current understanding of the mechanism of earthquakes originating on the MHT. (c) 2015 Elsevier Ltd. All rights reserved.

[1]  R. Briggs,et al.  Eight Days in Bhuj: Field Report Bearing on Surface Rupture and Genesis of the 26 January 2001 Earthquake in India , 2001 .

[2]  W. Korn.  The Traditional Architecture of the Kathmandu Valley , 1979 .

[3]  K. Whipple,et al.  Neotectonics of the central Nepalese Himalaya: Constraints from geomorphology, detrital 40Ar/39Ar thermochronology, and thermal modeling , 2006 .

[4]  L. Bollinger,et al.  Primary surface ruptures of the great Himalayan earthquakes in 1934 and 1255 , 2012, Nature Geoscience.

[5]  L. R. West,et al.  Observed effects of topography on ground motion , 1973, Bulletin of the Seismological Society of America.

[6]  Gautam Mitra,et al.  Thrust geometries and deep structure of the outer and lesser Himalaya, Kumaon and Garhwal (India): Implications for evolution of the Himalayan fold‐and‐thrust belt , 1994 .

[7]  S. Wesnousky,et al.  Earthquake Recurrence and Rupture Dynamics of Himalayan Frontal Thrust, India , 2001, Science.

[8]  Katsuichiro Goda,et al.  The 2015 Gorkha Nepal Earthquake: Insights from Earthquake Damage Survey , 2015, Front. Built Environ..

[9]  Masanobu Shimada,et al.  Line‐of‐sight displacement from ALOS‐2 interferometry: Mw 7.8 Gorkha Earthquake and Mw 7.3 aftershock , 2015 .

[10]  Wei-Xin Ren,et al.  Dynamic and seismic performance of old multi-tiered temples in Nepal , 2003 .

[11]  S. Mukherjee.  A review on out-of-sequence deformation in the Himalaya , 2015, Special Publications.

[12]  B. Bookhagen,et al.  Along-strike changes in Himalayan thrust geometry: Topographic and tectonic discontinuities in western Nepal , 2015 .

[13]  M. Salby,et al.  Relationship of the quasi-biennial oscillation to the stratospheric signature of the solar cycle , 2006 .

[14]  Roger Bilham,et al.  LOCATION AND MAGNITUDE OF THE 1833 NEPAL EARTHQUAKE AND ITS RELATION TO THE RUPTURE ZONES OF CONTIGUOUS GREAT HIMALAYAN EARTHQUAKES , 1995 .

[15]  K. Hodges,et al.  Active out-of-sequence thrust faulting in the central Nepalese Himalaya , 2005, Nature.

[16]  G. Gehrels,et al.  Eocene‐early Miocene foreland basin development and the history of Himalayan thrusting, western and central Nepal , 1998 .

[17]  J. Freymueller,et al.  GPS measurements of present-day convergence across the Nepal Himalaya , 1997, Nature.

[18]  Timothy P. Loomis,et al.  Tertiary mantle diapirism, orogeny, and plate tectonics east of the Strait of Gibraltar , 1975 .

[19]  Takashi Nakata,et al.  Paleoseismological evidence of surface faulting along the northeastern Himalayan front, India: Timing, size, and spatial extent of great earthquakes , 2010 .

[20]  R. J. Lillie,et al.  Contemporary tectonics of the Himalayan frontal fault system: folds, blind thrusts and the 1905 Kangra earthquake , 1991 .

[21]  Pascal Willis,et al.  Plate Motion of India and Interseismic Strain in the Nepal Himalaya from GPS and DORIS Measurements , 2006 .

[22]  Hiroyuki Tsutsumi,et al.  Surface Rupture of the 2005 Kashmir, Pakistan, Earthquake and Its Active Tectonic Implications , 2006 .

[23]  B. N. Upreti,et al.  Seismites in the Kathmandu basin and seismic hazard in central Himalaya , 2011 .

[24]  Pierre-Yves Bard,et al.  THE EFFECT OF TOPOGRAPHY ON EARTHQUAKE GROUND MOTION: A REVIEW AND NEW RESULTS , 1988 .

[25]  Jean-Philippe Avouac,et al.  Seismotectonics of the Nepal Himalaya from a local seismic network , 1999 .

[26]  Francis T. Wu,et al.  Seismicity and one-dimensional velocity structure of the Himalayan collision zone: Earthquakes in the crust and upper mantle , 2006 .

[27]  Leonardo Seeber,et al.  Great Detachment Earthquakes Along the Himalayan Arc and Long‐Term Forecasting , 2013 .

[28]  K. Hodges.  A synthesis of the Channel Flow-Extrusion hypothesis as developed for the Himalayan-Tibetan orogenic system , 2006, Geological Society, London, Special Publications.

[29]  D. Fink,et al.  Geomorphology reveals active décollement geometry in the central Himalayan seismic gap , 2015 .

[30]  B. John,et al.  Medieval pulse of great earthquakes in the central Himalaya: Viewing past activities on the frontal thrust , 2015 .

[31]  A. Okada,et al.  Timing and displacement of holocene faulting on the median tectonic line in central shikoku, southwest japan , 1991 .

[32]  T. Harrison,et al.  A Late Miocene-Pliocene origin for the Central Himalayan inverted metamorphism: Earth and Planetary , 1992 .

[33]  K. Whipple,et al.  Southward extrusion of Tibetan crust and its effect on Himalayan tectonics , 2001 .

[34]  Jérôme Lavé,et al.  Interseismic strain accumulation on the Himalayan crustal ramp (Nepal) , 1995 .

[35]  James Ni,et al.  Seismotectonics of the Himalayan Collision Zone: Geometry of the underthrusting Indian Plate beneath the Himalaya , 1984 .

[36]  Alexander L. Densmore,et al.  Topographic fingerprints of bedrock landslides , 2000 .

[37]  C. Rajendran,et al.  The status of central seismic gap: a perspective based on the spatial and temporal aspects of the large Himalayan earthquakes , 2005 .

[38]  C. Thorne,et al.  Quantitative analysis of land surface topography , 1987 .

[39]  B. N. Upreti,et al.  Structural interpretation of the great earthquakes of the last millennium in the central Himalaya , 2013 .

[40]  R. Bilham,et al.  Constraints on Himalayan deformation inferred from vertical velocity fields in Nepal and Tibet , 1994 .

[41]  K. Hodges,et al.  Tectonic evolution of the central Annapurna Range, Nepalese Himalayas , 1996 .

[42]  V. Gornitz,et al.  River profiles along the Himalayan arc as indicators of active tectonics , 1983 .

[43]  Kip V. Hodges,et al.  Has focused denudation sustained active thrusting at the Himalayan topographic front , 2003 .

[44]  J. Avouac.  Mountain Building: From Earthquakes to Geologic Deformation , 2015 .

[45]  Jérôme Lavé,et al.  Active folding of fluvial terraces across the Siwaliks Hills, Himalayas of central Nepal , 2000 .

[46]  S. Sapkota,et al.  Evidence for a Great Medieval Earthquake (~1100 A.D.) in the Central Himalayas, Nepal , 2005, Science.

[47]  S. Wesnousky,et al.  Uplift and convergence along the Himalayan Frontal Thrust of India , 1999 .

[48]  F. Cotton,et al.  Rupture history and seismotectonics of the 1991 Uttarkashi, Himalaya earthquake , 1996 .