THE SLIP DISTRIBUTION OF THE 1992 NICARAGUA EARTHQUAKE FROM TSUNAMI RUN-UP DATA

The 2 September 1992 Nicaragua tsunami was induced by an M(S) similar or equal to 7 - 7.3 earthquake and caused about 170 victims and signif icant damage to the coastal areas. The aim of this work is to infer th e slip distribution along the causative seismic fault from the availab le tsunami run-up field data. We have subdivided the fault plane into five slip-independent subfaults and computed the corresponding numeric al Green's functions by integrating shallow-water equations via a fini te-element technique. The slip distribution on the fault has been dete rmined by applying a least-squares procedure to the differences betwee n the observed run-up values and the computed maximum water levels alo ng the coast. The main result is that the best fit is found for a nonu niform coseismic slip, with the highest displacement taking place in t he southernmost part of the fault. The measure of the improvement is g iven by the global rms residual of the heterogeneous-slip case being c irca 25% smaller than that of the uniform case. An ancillary outcome o f the analysis is the evaluation of the mean amplification factor of t he tsunami wave investing the Nicaraguan coast, that, on assuming a ri gidity of 1 x 10(10) N/m(2), results to be 3.45.