Effects of site response on earthquake hazard in the eastern Marmara region of Turkey.

摘要

As part of a broader investigation of earthquake hazard, aftershocks of the 1999 Izmit (Mw = 7.4) and 12 November 1999 Duzce (Mw = 7.2) earthquakes are analyzed to investigate local site effects in eastern Marmara (Turkey) region. Seismic data used in this study were collected by the United States Geological Survey (USGS). Nearby stations were paired to calculate soft-soil to rock (or stiff-soil) relative amplifications for various aftershocks. Selected aftershocks were used to estimate the soil amplifications and to test a new application of slowness-frequency imaging for determining spectral amplifications over the entire signal to assess site effects on observed ground motions. Soft-soil ground motions are found to exceed those at nearby rock or stiff soil sites by factors of three or more in some cases for frequencies below approximately 12 Hz, but are significantly less than rock sites for frequencies above about 15 Hz, likely due to low Q (high attenuation) in the soil column.; When site-specific velocity structure information is available (e.g. from receiver-function estimates, geophysical surveys, borehole measurements) the site amplification effects can be modeled for comparison to the observed amplifications. Modeling results comparing non-linear behavior for nearby large earthquakes to linear behavior for small earthquakes shows that relative amplifications for small events gives an upper bound for large events. This allows the use of abundant small events to determine site effects in the study area.