Stress buildup in the Himalaya

The seismic cycle on a major fault involves long periods of elastic strain and stress accumulation, driven by aseismic ductile deformation at depth, ultimately released by sudden fault slip events. Coseismic slip distributions are generally heterogeneous with most of the energy being released in the rupture of asperities. Since, on the long term, the fault's walls generally do not accumulate any significant permanent deformation, interseismic deformation might be heterogeneous, revealing zones of focused stress buildup. The pattern of current deformation along the Himalayan arc, which is known to produce recurring devastating earthquakes, and where several seismic gaps have long been recognized, might accordingly show significant lateral variations, providing a possible explanation for the uneven microseismic activity along the Himalayan arc. By contrast, the geodetic measurements show a rather uniform pattern of interseismic strain, oriented consistently with long-term geological deformation, as indicated from stretching lineation. We show that the geodetic data and seismicity distribution are reconciled from a model in which microseismicity is interpreted as driven by stress buildup increase in the interseismic period. The uneven seismicity pattern is shown to reflect the impact of the topography on the stress field, indicating low deviatoric stresses (<35 MPa) and a low friction (<0.3) on the Main Himalayan Thrust. Arc-normal thrusting along the Himalayan front and east-west extension in southern Tibet are quantitatively reconciled by the model.

[1]  D. Schelling,et al.  Thrust tectonics, crustal shortening, and the structure of the far-eastern Nepal Himalaya , 1991 .

[2]  M. Brunel.  Ductile thrusting in the Himalayas : shear sense criteria and stretching lineations , 1986 .

[3]  Wenjin Zhao,et al.  Deep seismic reflection evidence for continental underthrusting beneath southern Tibet , 1993, Nature.

[4]  X. Pichon,et al.  Full interseismic locking of the Nankai and Japan‐west Kurile subduction zones: An analysis of uniform elastic strain accumulation in Japan constrained by permanent GPS , 2000 .

[5]  G. King,et al.  STATIC STRESS CHANGES AND THE TRIGGERING OF EARTHQUAKES , 1994 .

[6]  Rémi Michel,et al.  Horizontal coseismic deformation of the 1999 Chi-Chi earthquake measured from SPOT satellite images: Implications for the seismic cycle along the western foothills of central Taiwan , 2003 .

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

[8]  H. Kanamori,et al.  Temporal variation of large intraplate earthquakes in coupled subduction zones , 1989 .

[9]  Jean-Philippe Avouac,et al.  On the use of dislocations to model interseismic strain and stress build-up at intracontinental thrust faults , 2001 .

[10]  Kelin Wang,et al.  Thermal constraints on the zone of major thrust earthquake failure: The Cascadia Subduction Zone , 1993 .

[11]  É. Calais,et al.  Geodetic observations of interseismic strain segmentation at the Sumatra Subduction Zone , 1997 .

[12]  Paul Segall,et al.  Rapid afterslip following the 1999 Chi‐Chi, Taiwan Earthquake , 2002 .

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

[14]  Rodolphe Cattin,et al.  Modeling mountain building and the seismic cycle in the Himalaya of Nepal , 2000 .

[15]  J. Freymueller,et al.  Spatial variations in present‐day deformation, Kenai Peninsula, Alaska, and their implications , 2000 .

[16]  J. Avouac,et al.  Oblique convergence in the Himalayas of western Nepal deduced from preliminary results of GPS measurements , 1999 .

[17]  T. Nakata,et al.  Active faults of the Himalaya of India and Nepal , 1989 .

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

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

[20]  Y. Okada.  Internal deformation due to shear and tensile faults in a half-space , 1992, Bulletin of the Seismological Society of America.

[21]  R. Bürgmann,et al.  Kinematics of the India-Eurasia collision zone from GPS measurements , 1999 .

[22]  P. Molnar,et al.  Focal depths and fault plane solutions of earthquakes under the Tibetan plateau , 1983 .

[23]  B. N. Upreti,et al.  Stratigraphy, structure, and tectonic evolution of the Himalayan fold‐thrust belt in western Nepal , 2001 .

[24]  A. Pêcher.  The contact between the Higher Himalaya Crystallines and the Tibetan Sedimentary Series: Miocene large‐scale dextral shearing , 1991 .

[25]  Kelin Wang,et al.  The updip and downdip limits to great subduction earthquakes: Thermal and structural models of Casca , 1999 .

[26]  J. Rice,et al.  Seismicity and deformation at convergent margins due to heterogeneous coupling , 1996 .

[27]  Paul Segall,et al.  Fault geometry and slip distribution of the 1999 Chi‐Chi, Taiwan Earthquake imaged from inversion of GPS data , 2001 .

[28]  P. Molnar,et al.  Fault plane solutions of earthquakes and active tectonics of the Tibetan Plateau and its margins , 1989 .

[29]  J. Avouac,et al.  Current shortening across the Himalayas of Nepal , 2004 .

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

[31]  P. Molnar,et al.  Focal depths and fault plane solutions of earthquakes and active tectonics of the Himalaya , 1984 .

[32]  E. Dutton,et al.  Reply [to Comment on A long term decrease in arctic haze at Barrow, Alaska by B.A. Bodhaine and E , 1995 .

[33]  J. C. Savage.  A dislocation model of strain accumulation and release at a subduction zone , 1983 .

[34]  Kelin Wang,et al.  A Silent Slip Event on the Deeper Cascadia Subduction Interface , 2001, Science.

[35]  Bor‐Shouh Huang.  Evidence for azimuthal and temporal variations of the rupture propagation of the 1999 Chi‐Chi, Taiwan Earthquake from dense seismic array observations , 2001 .

[36]  Peter Molnar,et al.  Himalayan Seismic Hazard , 2001, Science.

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