[S03-P] Poster

[S03-P-02] Spatial variations of intrinsic absorption and scattering loss in Taiwan based on a Multiple Lapse Time Window Analysis

^○Kevin Gillet¹, Ludovic Margerin¹, Shu-Huei Hung², Marie Calvet¹ (1.IRAP - University of Toulouse, Toulouse, France, 2.Department of Geosciences, National Taiwan University, Taipei, Taiwan)

We use seismic recordings from 2012 to 2015 to estimate intrinsic absorption and scattering loss in Taiwan. Signals were recorded by a network of about 150 stations. About 400 events of magnitude between 3.5 and 6.5 and 4000 events of magnitude between 1.8 and 3.5 were recorded per year. We use the Multiple Lapse Time Window Analysis introduced by Fehler et al. (1992) to measure integrals of energy in different windows in the coda of the signals, selecting events with hypocentral distances below 100 km and sources less than 40 km deep. These measurements, which represent the temporal distribution of the energy in the coda, can be used to separate the two components of attenuation, absorption and scattering. An inversion using a Levenberg-Marquardt algorithm is performed to find estimates of the absorption and scattering quality factors Qi-1 and Qsc-1, for each station considered. We find that Taiwan is one the most highly attenuating regions in the world, with an average of Qsc-1 = 1e-2 and Qi-1 = 7e-3 at 1-2 Hz. Another important feature is that attenuation varies widely across Taiwan, by a factor of 3 for total attenuation. We find that the eastern Coastal Range and parts of the western Coastal Plain are the most highly attenuating regions of Taiwan. However, the region surrounding the Peikang Basement High and parts of northern Taiwan are more weakly attenuating, which increases risk for the cities in this region. Overall, intrinsic absorption is more uniform than scattering loss. The Coastal Plain shows strong scattering. The Coastal Range shows strong scattering and absorption, consistent with the volcanic origin of the structures. Scattering in the Central Range seems weaker than in these two regions. Our study shows that attenuation should be taken into account for seismic studies and monitoring in Taiwan, given the importance and lateral variability of the mechanism.