Browsing by Author "Imtiyaz A. Parvez"

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Body-wave wave-form modelling and source parameters for the indochina border earthquakes
(Birkhauser Verlag AG, 1996) Imtiyaz A. Parvez; Avadh Ram
Wave-form modelling of body waves has been done to study the seismic source parameters of three earthquakes which occurred on October 21, 1964 (Mb,-5.9), September 26, 1966 (Mb = 5.8) and March 14, 1967 (Mb = 5.8). These events occurred in the Indochina border region where a low-angle thrust fault accommodates motion between the underthrusting Indian plate and overlying Himalaya. The focal depths of all these earthquakes are between 12-37 km. The total range in dip for the three events is 5°-20°. The T axes are NE-SW directed whereas the strikes of the northward dipping nodal planes are generally parallel to the local structural trend. The total source durations have been found to vary between 5-6 seconds. The average values of seismic moment, fault radius and dislocation are 1.0-11.0 × 1025 dyne-cm, 7.7-8.4 km and 9.4-47.4 cm, respectively whereas stress drop, apparent stress and strain energy are found to be 16-76 bars, 8.2-37.9 bars and 0.1 - 1.7 × 1021 ergs, respectively. These earthquakes possibly resulted due to the tension caused by the bending of the lithospheric plate into a region of former subduction which is now a zone of thrusting and crustal shortening.
Probabilistic assessment of earthquake hazards in the Indian subcontinent
(Birkhauser Verlag AG, 1999) Imtiyaz A. Parvez; Avadh Ram
The Indian subcontinent is one of the most seismic prone areas of the world. The Himalayan mountains in the north, mid-oceanic ridges in the south and earthquake belts surrounding the Indian plate all show that the subcontinent has undergone extensive geological and tectonic processes in the past. The probability of the occurrence of earthquakes with magnitude 6 < M(b) < 7 during a specified interval of time has been estimated on the basis of four probabilistic models namely Lognormal, Weibull, Gamma and Exponential distribution for the Indian subcontinent. The seismicity map has been prepared using the earthquake catalogue from the period 1963-1994, and six different zones have been identified on the basis of clustering of events. The model parameters have been estimated by the method of maximum likelihood estimates (MLE) and method of moments (MOM). A computer program package has been developed for all four models, which represents the distributions of time intervals fairly well. The logarithmic of likelihood (1n L) is estimated for testing the models and different models have been found to be plausible. The probability of different magnitude thresholds has been evaluated using the Gutenberg-Richter formula Log N = a - bM for magnitude distribution. The constants a and b have been computed for each region and found to be varying between 5.46-8.53 and 0.87-1.34, respectively.
Probabilistic assessment of earthquake hazards in the North-East Indian peninsula and Hindukush regions
(Birkhauser Verlag AG, 1997) Imtiyaz A. Parvez; Avadh Ram
The Himalayan region is one of the most seismic prone areas of the world. The North-East (NE) Indian peninsula and the Hindukush regions mark the zone of collision of the Indian and Eurasian plates. The probability of the occurrence of great earthquakes with magnitude greater than 7-0 during a specified interval of time has been estimated on the basis of four probabilistic models, namely, Weibull, Gamma, Lognormal and Exponential for the NE Indian peninsula and Hindukush regions. The model parameters have been estimated by the method of Maximum Likelihood Estimates (MLE) and the Method of Moments (MOM). The cumulative probability is estimated for a period of 40 years from 1964 and is ranging between 0.881 to 0.995 by the year 1995. using all four models for the NE Indian peninsula. The conditional probability is also estimated and it is concluded that the NE Indian peninsula would expect a great earthquake at any time in the remaining years of the present century. For the Hindukush region, the cumulative probability has already crossed its highest value, but no earthquake of magnitude greater than 7.0 has occurred after 1974 in this area. It may attribute to the occurrence of frequent shocks of moderate size, as seventeen earthquakes of magnitude greater than 6.0, including four greater than 6.4, have been reported until 1994 from this region.