SELF CONSISTENT SCALING LAWS FOR THE HIMALAYAS

Abstract

The Great Himalayan arc being the highest mountain ranges in the world, are the result of collision between the Indian and the Eurasian plate. The region is seismically very active owing to continued convergence. They are aptly the highest, youngest and among the best studied continental orogenic belts in the world. This mountain belt provides a natural laboratory set up for the engineers and scientists for their research pursuits. The Himalayan region is known to undergo non uniform convergence and due to this the process of strain energy accumulation varies spatially and temporally. This strain energy subsequently releases in the form of earthquakes of varied sizes including great ones resulting in devastating damages. The assessment of the forces (strong ground motion) generated by the damaging earthquakes in future is required to safe guard the built environment. Earthquake potential assessment require the knowledge of fault geometry parameters (rupture length, rupture width, rupture area, etc.), which are important inputs to seismic hazard analyses using any of the approaches namely, probabilistic and/or deterministic. Many researchers have developed empirical relationships between earthquake magnitude and fault parameters using statistical analyses. Various empirical relationships developed throughout the world show inconsistency in the estimation of rupture geometrical parameters from magnitude and vice versa. This necessitates a comprehensive study to develop consistent relationships for the rupture parameters and the size of the earthquakes. Such inconsistency is not only present in the form of estimating the parameters using different routes i.e., from one parameter of geometry to another and then to size and vice versa, but also using the same parameters as independent and/or dependent variables. Such behaviour may affect the end result in the form of strong ground motion estimation and necessitates the solutions in terms of consistent empirical relationships among the various source parameters and size in terms of magnitude. The relations that enable seismic moment, fault length, width, area to be estimated from each other, with all these relations being consistent with the seismic moment, are termed as self-consistent relations. The main objective of this research was to critically revisit empirical relationships between various fault parameters in different seismotectonic environments and to develop self-consistent scaling relationship between moment magnitude and fault parameters for the Himalayan region.