Abnormal intensities distributions in subduction zone
Speaker: Mu-Ching Liu
Abstract
When an earthquake occurs, people close to epicenter feel strong motion than others, because energy decreases gradually as epicenter distance increase. However, we find many earthquakes which their intensity patterns don¡¦t obey this pattern in Japan. The abnormal intensities distributions are probably caused by regional differences in absorption of seismic waves, a region of absorption has located in the upper mantle under Japan outside the zone of abnormal intensity. This phenomenon also appears in New Zealand. Because we lack strong motion data which seismic ray pass through highly attenuation mantle zone , we cannot use the standard New Zealand response spectral acceleration model to predict the earthquakes¡¦ strong motion exactly. We use 3D-Q model to modify response spectral acceleration model. This modification reduce the spectra for mantle wedge path, and the reduction is similar to the observed variation in response spectra, so this approach may be useful in other situations where there is limited availability of strong motion data.
Reference
Phillips, D. E. , and McVerry, G., Estimating Slab Earthquake Response Spectra from a 3D Q Model, Bulletin of the Seismological Society of America, Vol. 93, No. 6, pp. 2649-2663, December 2003.
UTSU, T. Regional Differences in Absorption of Seismic Waves in the Upper Mantle as Inferred from Abnormal Distributions of Seismic Intensities, Journal of the Faculty of Science, Hokkaido University, Japan, Ser. VII, Vol II, No. 4, 1966.