INITIAL GEOLOGICAL AND ENGINEERING ASSESSMENT OF THE 2015 NEPAL, GORKHA M7.8 EARTHQUAKE AND ITS SOCIETAL AFTERMATH

An Mw 7.8 earthquake struck Nepal on April 25, 2015 at 11:56 local time. The shock was felt throughout Nepal and in India, Bangladesh and Tibet. Along with its largest Mw 7.3 aftershock on May 12, it severely affected 14 Nepal districts resulting in 8891 fatalities, 22303 injuries, millions of homeless, earthquake environmental effects (EEE), damage on buildings and infrastructures and great economic losses. Based on field reconnaissance in the affected area immediately after the main shock, primary EEE were not detected, while secondary EEE included slope movements, liquefaction, ground cracks and hydrological anomalies especially in the Kathmandu valley suggesting a combination of directivity and deep basin effects. Masonry and cultural heritage structures suffered most damage due to inadequate construction and poor maintenance. In case of sounder construction, such buildings remained intact. Most of reinforced concrete buildings weathered the earthquake without damage despite of possessing high seismic vulnerability in most cases. The earthquake response of buildings was discontinuously nonlinear. It was observed that either partial or total collapse or no horizontal motion, no cracks, no breaking of glass window panels occurred. This fact is a key characteristic of the local domination of vertical excitation and the respective response of structures.

[1]  Active faulting across the Himalaya and its significance in the collision tectonics , 2002 .

[2]  D. Gautam,et al.  Seismic Hazard in the Himalayan Intermontane Basins: An Example from Kathmandu Valley, Nepal , 2015 .

[3]  Brian D. Collins,et al.  Geotechnical Effects of the 2015 Magnitude 7.8 Gorkha, Nepal, Earthquake and Aftershocks , 2015 .

[4]  Brian D. Collins,et al.  Assessment of existing and potential landslide hazards resulting from the April 25, 2015 Gorkha, Nepal earthquake sequence. , 2015 .

[5]  Eric J. Fielding,et al.  Field Reconnaissance after the 25 April 2015 M 7.8 Gorkha Earthquake , 2015 .

[6]  B. N. Upreti,et al.  LESSER HIMALAYAN CRYSTALLINE NAPPES OF NEPAL : PROBLEMS OF THEIR ORIGIN , 1999 .

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

[8]  J. Mugnier,et al.  Frontal and piggy-back seismic ruptures in the external thrust belt of Western Nepal☆ , 2005 .

[9]  A. Sengor.  Paleotectonics of Asia : fragments of a synthesis. , 1996 .

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

[11]  Lin Ding,et al.  Convergence rate across the Nepal Himalaya and interseismic coupling on the Main Himalayan Thrust: Implications for seismic hazard , 2011 .

[12]  J. Avouac,et al.  Le cycle sismique en Himalaya , 2001 .

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

[14]  M. Dhital.  Geology of the Nepal Himalaya: Regional Perspective of the Classic Collided Orogen , 2015 .

[15]  Yoann Cano,et al.  The aftershock sequence of the 2015 April 25 Gorkha–Nepal earthquake , 2015 .

[16]  P. Pandey.  Letter from Nepal, August 12, 2015--Cholera in post-earthquake Kathmandu. , 2015, Travel medicine and infectious disease.

[17]  N. Bhandary,et al.  Report on a reconnaissance survey of damage in Kathmandu caused by the 2015 Gorkha Nepal earthquake , 2015 .

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

[19]  M. Searle,et al.  Defining the Himalayan Main Central Thrust in Nepal , 2008, Journal of the Geological Society.

[20]  J. Galetzka,et al.  Slip pulse and resonance of the Kathmandu basin during the 2015 Gorkha earthquake, Nepal , 2015, Science.

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

[22]  D. Rowley.  Age of initiation of collision between India and Asia: A review of stratigraphic data , 1996 .