Accounting for source effects in the shakemap procedure: The 2000 tottori and the 2008 miyagi earthquakes

Abstract

Real-time seismology has made significant improvements in recent years, with source parameters now available within a few tens of minutes after an earthquake. It is likely that this time will be further reduced, in the near future, by means of increased efficiency in real-time transmission, increasing data coverage and improvement of the methodologies. In this context, together with the development of new ground motion predictive equations (GMPEs) that are able to account for source complexity, the generation of strong ground motion shaking maps in quasi-real time has become ever more feasible after the occurrence of a damaging earthquake. However, GMPEs may not reproduce reliably the ground motion in the near-source region where the finite fault parameters have a strong influence on the shaking. In this paper we test whether accounting for source-related effects is effective in better characterizing the ground motion.We introduce a modification of the GMPEs within the ShakeMap software package, and subsequently test the accuracy of the newly generated shakemaps in predicting the ground motion. The test is conducted by controlling the performance of ShakeMap as we decrease the amount of the available information. We then update ShakeMap with the GMPE modified with a corrective factor accounting for source effects, in order to better constrain these effects that likely influence the level of (near-source) ground shaking. We investigate two well-recorded earthquakes from Japan (the 2000 Tottori, Mw 6.6, and the 2008 Iwate-Miyagi, Mw7.0, events) where the instrumental coverage is as dense as needed to ensure an objective appraisal of the results. The results demonstrate that the corrected GMPE can capture only some aspects of the ground shaking in the near-source area, neglecting other multidimensional effects, such as propagation effects and local site amplification. © The Authors 2013. Published by Oxford University Press on behalf of The Royal Astronomical Society.