Determination of Epicenter and Comparison of some Empirical Formulae with Observed Data of Acceleration from Two Events in Himalaya

Two earthquakes of April 26 and September 10 were recorded by strong motion array's in India during the year 1986 by Kangra and ShilIoog array respectively. Mean peak horizontal accelerations are in the range of 157 to 2217 mm/sec in case of the April event, whereas it is 163 to 1234 rnmlsec2 for the September one.

Epicentral information (DEQ) has been derived using P and S wave arrival times of strong motion accelerograph stations and compared with that reported by IMD and USGS. Epicentral distance and focal depth are better indicated by the strong motion array data. Focal parameter obtained for the earthquakes differ from that reported by USGS. For the April earthquake, USGS epicenter (E2) lies around 10 km southeast of DEQ epicenter (E3). Focal depth obtained 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 around 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 formulae were used to estimate acceleration at a particuIar site. For the April event McGuire's estimate is very close to tbe observed acceleration when DEQ hypocenter was taken into consideration. However, accelerations estimated for the September event do not conform to the observed ones, eventhough some values are quite cIose.