[S-EM14] Electric, magnetic and electromagnetic survey technologies and scientific achievements

[SEM14-14] 1-D Electrical Conductivity Variation Beneath Taiwan Derived from C-responses Estimation

*Ding-Jiun Lin^1,2, Ping-Yu Chang^1,3 (1.NCU, TW., 2.CTGS., 3.E-DREaM.)

Keywords:C-response, geomagnetic depth sounding, electrical structure, mantle

Taiwan is situated on the convergence boundary of the Eurasian and Philippine Sea plates. Although there are several studies focusing on the shallow structure of Taiwan. However, the study of the structure beneath the 200km depth is still absent. Therefore, we estimate the C-response of the geomagnetic depth sounding (GDS) to study the deeper structure beneath Taiwan. C-response is the response function to describe the geomagnetic variation, which connects the magnetic vertical component and the horizontal gradient of the horizontal components. We analyzed several geomagnetic observatories, the longest geomagnetic data is 12 years, which was recorded by Lunping (LNP) geomagnetic observatory in northern Taiwan. To estimate the C-response, we remove the secular variation from the original time-series data. Then we estimate the response function by assuming the geomagnetic field spatial variations are adequately described by a simple spherical harmonic, P¹₀. Furthering, we calculate the apparent resistivity from the derived C-response from different periods. Moreover, we inverse to the 1-D conductivity result by applying Occam inversion. The conductivity model shows the increasing of conductivity trend from 0.02 S/m near 200 km to 3 S/m at 900 km depth. Also, the results reveal a significant increase from 0.01 S/m to 0.3 S/m at 426 km depth and 660 km depth, which might correspond to the mantle transition zone of the upper mantle and lower mantle below northern Taiwan.