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The Coimbatore corporation area is comprised of very densely occupied residential and commercial buildings which are prone to future earthquakes. Probabilistic Seismic Hazard Analysis (PSHA) was carried out for the study region using the Classical Cornell approach and the logic-tree approach. A combination of 45 linear/fault sources and an areal source with a 500 km radius has been considered for the study. An updated earthquake catalogue has been compiled from various works of literature and authorized organizations. The collected earthquake catalogue of various magnitude scales has been homogenized into a uniform moment magnitude scale M w . Fore-shocks and after-shocks have been removed from independent events using one of the declustering algorithms. The seismicity parameters have been evaluated using the Guttenberg–Richter recurrence law. A hybrid GMPE composed of three attenuation relationships was used to obtain the ground motion parameters for the study region. The contour maps of Peak Ground Acceleration (PGA) and Peak Spectral Acceleration (PSA) for the bed-rock condition have been presented in terms of 10 and 2% Probability of Exceedance (PoE) for the return period of 475 and 2475 yr, respectively. The Uniform Hazard Response Spectra (UHRS) for Coimbatore city has been compared with (IS 1893-I-(2016) Criteria for earthquake resistant design of structures. Part 1: General provisions and buildings; Bureau of Indian Standards). As a result of deaggregation, the predominant hazard has been found within a 100 km distance and no hazards have been observed from a long distance as a controlling scenario from the analysis. [ABSTRACT FROM AUTHOR]

Data collected at approximately 60 Global Positioning System (GPS) sites in southeast Asia show the crustal deformation caused by the 26 December 2004 Sumatra-Andaman earthquake at an unprecedented large scale. Small but significant co-seismic jumps are clearly detected more than 3,000 km from the earthquake epicentre. The nearest sites, still more than 400 km away, show displacements of 10 cm or more. Here we show that the rupture plane for this earthquake must have been at least 1,000 km long and that non-homogeneous slip is required to fit the large displacement gradients revealed by the GPS measurements. Our kinematic analysis of the GPS recordings indicates that the centroid of released deformation is located at least 200 km north of the seismological epicentre. It also provides evidence that the rupture propagated northward sufficiently fast for stations in northern Thailand to have reached their final positions less than 10 min after the earthquake, hence ruling out the hypothesis of a silent slow aseismic rupture.

Directivity effects are a characteristic of seismic source finiteness and are a consequence of the rupture spread in preferential directions. These effects are manifested through seismic spectral deviations as a function of the observation location. The directivity by Doppler effect method permits estimation of the directions and rupture velocities, beginning from the duration of common pulses, which are identified in waveforms or relative source time functions. The general model of directivity that supports the method presented here is a Doppler analysis based on a kinematic source model of rupture (Haskell, Bull Seismol Soc Am 54:1811–1841, ) and a structural medium with spherical symmetry. To evaluate its performance, we subjected the method to a series of tests with synthetic data obtained from ten typical seismic ruptures. The experimental conditions studied correspond with scenarios of simple and complex, unilaterally and bilaterally extended ruptures with different mechanisms and datasets with different levels of azimuthal coverage. The obtained results generally agree with the expected values. We also present four real case studies, applying the method to the following earthquakes: Arequipa, Peru ( Mw = 8.4, June 23, 2001); Denali, AK, USA ( Mw = 7.8; November 3, 2002); Zemmouri–Boumerdes, Algeria ( Mw = 6.8, May 21, 2003); and Sumatra, Indonesia ( Mw = 9.3, December 26, 2004). The results obtained from the dataset of the four earthquakes agreed, in general, with the values presented by other authors using different methods and data. [ABSTRACT FROM AUTHOR]

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