A homogenous earthquake catalog is a basic input for seismic hazard estimation, and other seismicity studies. The preparation of a homogenous earthquake catalog for a seismic region needs regressed relations for conversion of different magnitudes types, e.g. m b , M s , to the unified moment magnitude M w. In case of small data sets for any seismic region, it is not possible to have reliable region specific conversion relations and alternatively appropriate global regression relations for the required magnitude ranges and focal depths can be utilized. In this study, we collected global events magnitude data from ISC, NEIC and GCMT databases for the period 1976 to May, 2007. Data for m b magnitudes for 3,48,423 events for ISC and 2,38,525 events for NEIC, M s magnitudes for 81,974 events from ISC and 16,019 events for NEIC along with 27,229 M w events data from GCMT has been considered. An epicentral plot for M w events considered in this study is also shown. M s determinations by ISC and NEIC, have been verified to be equivalent. Orthogonal Standard Regression (OSR) relations have been obtained between M s and M w for focal depths (h \ 70 km) in the magnitude ranges 3.0 B M s B 6.1 and 6.2 B M s B 8.4, and for focal depths 70 km B h B 643 km in the magnitude range 3.3 B M s B 7.2. Standard and Inverted Standard Regression plots are also shown along with OSR to ascertain the validation of orthogonal regression for M s magnitudes. The OSR relations have smaller uncertainty compared to SR and ISR relations for M s conversions. ISR relations between m b and M w have been obtained for magnitude ranges 2.9 B m b B 6.5, for ISC events and 3.8 B m b B 6.5 for NEIC events. The regression relations derived in this study based on global data are useful empirical relations to develop homogenous earthquake catalogs in
This study derives ground-motion prediction equations for the horizontal elastic response spectral acceleration for 5% damping for application to the Indian Himalayas. The present equations include a consideration of site category (rock/soil) and style-of-faulting (strike-slip/reverse). Due to a lack of near-field data from India additional strong-motion data have been included from the Zagros region of Iran, which has comparable seismotectonics to the Himalayas (continental compression). A set of 201 records from 16 earthquakes were used within the regression. The derived model predicts similar ground motions to previously published equations for the Himalayan region but with lower standard deviations.
The seismically active Northwest (NW) Himalaya falls within Seismic Zone IV and V of the hazard zonation map of India. The region has suffered several moderate (*25), large-to-great earthquakes (*4) since Assam earthquake of 1897. In view of the major advancement made in understanding the seismicity and seismotectonics of this region during the last two decades, an updated probabilistic seismic hazard map of NW Himalaya and its adjoining areas covering 28-34°N and 74-82°E is prepared. The northwest Himalaya and its adjoining area is divided into nineteen different seismogenic source zones; and two different region-specific attenuation relationships have been used for seismic hazard assessment. The peak ground acceleration (PGA) estimated for 10% probability of exceedance in 50 and 10 years at locations defined in the grid of 0.25 9 0.25°. The computed seismic hazard map reveals longitudinal variation in hazard level along the NW Himalayan arc. The high hazard potential zones are centred around Kashmir region (0.70 g/0.35 g), Kangra region (0.50 g/0.020 g), Kaurik-Spitti region (0.45 g/0.20 g), Garhwal region (0.50 g/0.20 g) and Darchula region (0.50 g/0.20 g) with intervening low hazard area of the order of 0.25 g/0.02 g for 10% probability in 50 and 10 years in each region respectively.
The maximum likelihood estimation of earthquake hazard parameters has been made in the Himalayas and its surrounding areas on the basis of a procedure which utilizes data containing complete files of the most recent earthquakes. The entire earthquake catalogue used covers the period from 1900-1990. The maximum regional magnitude M max , the activity rate of the seismic event u, the mean return period R of earthquakes with a certain lower magnitude M max ]m along with their probability of occurrence, as well as the parameter b of of Gutenberg Richter magnitude-frequency relationship, have been determined for six different seismic zones of the Himalayas and its vicinity. It is shown that in general the hazard is higher in the zone NEI and BAN than the other four zones. The high difference of the b parameter and the hazard level from zone to zone reflect the high seismotectonic complexity and crustal heterogeneity.
SUMMARY
In this study, a procedure for the application of general orthogonal regression (GOR) towards conversion of different magnitude types is described. Through minimization of the squares of orthogonal residuals, GOR relation is obtained in terms of the abscissas (Mx*) of the projected points corresponding to the observed data pairs (Mx, obs, My, obs). In many studies, Mx* is replaced by Mx, obs in the GOR relation for convenience of obtaining the estimates of a preferred magnitude type for given magnitude values. Such forms of GOR, however, lead to biased estimates of the dependent variable. To represent the GOR relation correctly in terms of Mx, obs, a linear relation has been obtained between Mx* and Mx, obs using given points and the corresponding projected points on the GOR line.
Based on events data for the whole globe during the period 1976–2007, GOR relations have been derived for conversion of mb to Mw,mb to Ms,mb to Me and Ms to Mw following the proposed procedure and using specific error variance ratio (η) values. The superiority of the GOR relations obtained following the proposed procedure over the commonly used forms has been shown by computing the absolute average difference and standard deviation between the observed and the estimated values using events data not used in the derivation. It is observed that the proposed GOR relations yield better estimates compared to the commonly used GOR forms.
This procedure has been further tested for a wide range of η values between 0.1 and 7.0. The procedure proposed in this study can be used for the purpose of catalogue homogenization where GOR relations are applicable for conversion of different magnitude types.
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