DETERMINATION OF EPICENTER AND COMPARISON OF SOME EMPIRICAL FORMULAS WITH OBSERVED DATA OF ACCELERATION FROM 2 EVENTS IN HIMALAYA

Two earthquakes of April 26 and September 10 were recorded by strong m otion array's in India during the year 1986 by Kangra and Shillong arr ay respectively. Mean peak horizontal accelerations are in the range o f 157 to 2217 mm/sec2 in case of the April event, whereas it is 163 to 1234 mm/sec2 for the September one. Epicentral information (DEQ) has been derived using P and S wave arrival times of strong motion acceler ograph stations and compared with that reported by IMD and USGS. Epice ntral distance and focal depth are better indicated by the strong moti on array data. Focal parameter obtained for the earthquakes differ fro m that reported by USGS. For the April earthquake, USGS epicenter (E2) lies around 10 km southeast of DEQ epicenter (E3). Focal depth obtain ed in this study is only around 7 km against 33 km given by USGS. But in the case of the September event epicenter location by DEQ (E3) and USGS (E2) lie close to each other but focal depths were different arou nd 28 km (DEQ) against 43 km (USGS). Error parameters, like RMS, ERH, ERZ are very low in both the cases. McGuire's and other empirical form ulae were used to estimate acceleration at a particular site. For the April event McGuire's estimate is very close to the observed accelerat ion when DEQ hypocenter was taken into consideration. However, acceler ations estimated for the September event do not conform to the observe d ones, eventhough some values are quite close.