[SSS15-P23] Ground penetrating radar profiling across the Sanchiao fault in northeast Taiwan
Keywords:active fault, 1867 Keelung earthquake, Ground Penetrating Radar
The GPR survey was carried out on a coastal dune to the north of Jinshan. The coastal sand dune runs in a northwest-southeast direction along the shore, perpendicularly to the Sanchiao fault. The following two types of GPR survey lines were set up: a long range type (100-200 m) running parallel to the coastal dune, and a short range type (20 m) running perpendicularly to the coastal dune. Surveys were carried out from August 15-17, 2017 and from August 13-17, 2018. Three short lines were set up parallel to the dune and two lines perpendicularly to the dune. The pulseEKKO from Sensors & Software Inc. was used for the GPR survey, and the survey frequency of the radar was 50 MHz, 100 MHz, and 250 MHz.
A conspicuous radar reflector was found in the survey line running parallel to the coastal dune. The depth of this reflection changed near the fault trace of the Sanchiao fault, as estimated from boreholes. Furthermore, the depth of the reflection at the northwestern region of the fault was approximately 1 m deeper than that at the southeastern region. This is inconsistent with the vertical displacement of the normal faulting of the Sanchiao fault that dips southeastward, and suggests that the deformation could have been caused by the branching off of the splay fault from the main Sanchiao fault.