Accounting for source effects in the ShakeMap procedure: the 2000 Tottori and the 2008 Miyagi earthquakes

Abstract

Recently, there have been great improvements in real-time seismology. At present, source parameters are available within a few tens of minutes after the earthquake occurrence and there is an evidence that this time will be further reduced, in terms of efficiency of real time transmission and increasing data coverage. In this context, together with the development of new ground motion predictive equations (GMPEs) able to account for source complexity, the generation of maps of strong ground motion shaking in quasi real-time has become ever more feasible after the occurrence of a damaging earthquake. However, GMPEs may not reproduce faithfully the ground motion in the near source region if the finiteness of the causative fault is not taken into account. In this work, we test the effectiveness of refined GMPEs to improve the accuracy of the ShakeMap software package in the generation of the shakemaps. The test is conducted controlling the performance of ShakeMap as we decrease the amount of the available data. We then update ShakeMap with the equations derived within the NGA project (Power et al. 2008) in order to better constrain source effects that are likely to influence strongly the level of ground shaking. In order to conduct the test properly, we select an area as dense as needed to ensure an objective appraisal of the results. We investigate two well-recorded events from Japan: the 2008 Iwate-Miyagi (Mw7) and the 2000 Tottori (Mw6.6) events. The results outline that these equations can capture some aspects of the ground shaking, in particular the effects that depend the most on the earthquake source. Nevertheless, the huge scatter of real data respect to the distance from the source is not fully embedded inside the predictive equations, and the strong variability maybe attributable to other multidimensional effects, like propagation effects and local site amplification.