Testing the Density of Seismic Networks with ShakeMap

Zhifeng Hu, & Kim B. Olsen

Published August 15, 2017, SCEC Contribution #7690, 2017 SCEC Annual Meeting Poster #262

ShakeMap, developed by the U.S. Geological Survey, is an important tool used to assess the extent of ground motions after an earthquake, which can be used for loss estimation, public information, and emergency management efforts. Thus, the more accurately the ground shaking and damage can be captured by ShakeMap, the more effectively it can be used in these efforts. While the seismic station distribution in seismically active locations in the US provide a wealth of data that are used to generate ShakeMaps after an earthquake, instrumentation gaps are present. In order to generate ShakeMaps for regions under-represented by stations, Ground Motion Prediction Equations (GMPEs) are currently used to fill in the gaps. However, GMPEs introduce a great deal of uncertainty into the ShakeMap due to their smooth nature. Here, we use ‘data’ extracted from detailed dynamic rupture-based simulations of large earthquakes in selected areas (including southern California, the Pacific Northwest region and the Salt Lake Valley) to test the ability of the current networks to reproduce detailed shaking patterns. Preliminary results show that ShakeMap reproduces the major features in the simulated ground motions for a M7.8 scenario on the southern San Andreas Fault, including wave-guide effects near the Los Angeles basin using the current network of stations. This result is maintained even when up to 70% of randomly selected stations are disabled (simulating malfunction) in the LA basin. In the Pacific Northwest region, where station distribution in rural areas can be sparse, the shaking pattern in ShakeMap is not reproduced as clearly as in southern California. Yet ShakeMap can predict strong ground shaking near populous cities (Seattle and Portland) with much denser local stations, even for a simulated 60% station malfunction. The comparison in the Salt Lake Valley reveals ShakeMap’s ability to reproduce detailed shaking patterns in small regions deployed with a proportionally higher station density.

Citation
Hu, Z., & Olsen, K. B. (2017, 08). Testing the Density of Seismic Networks with ShakeMap. Poster Presentation at 2017 SCEC Annual Meeting.

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