Crustal structure in the middle-southern segments of the Tanlu Fault Zone and adjacent regions constrained by multifrequency receiver function and surface wave data

Abstract

We successively adopt H-k stacking of receiver functions (RFs) and joint inversion of RF and surface wave dispersion with Gaussian factors of 1.0, 2.0 and 3.0 to invert the crustal thickness (H), average Vp/Vs ratio (k) and S-wave velocity beneath 146 broadband seismic stations in the middle-southern segments of the Tanlu Fault Zone (TLFZ) and adjacent regions. These observations, together with previous geologic and geophysical studies, are further used to investigate Phanerozoic tectonic evolution in the study region and the seismogenic environment of the Tancheng Ms 8.5 earthquake. Our results show that the Moho depth and k generally range from 25 to 38 km and 1.65–1.95, respectively. The study region is roughly divided into three parts with different crustal structures from north to south, based on the Cretaceous Tiefogou fault and Triassic Lu'an fault and their extensional profiles, which may reflect different responses to the westward subduction of the Paleo-Pacific and Pacific Plates in the Mesozoic-Cenozoic. In addition to the observed uplifted Moho, high k and vertically alternating high-/low-velocity layers, lateral variations in S-wave velocity and junctions of multiple faults are imaged beneath the Tancheng earthquake zone, which may also contribute to the occurrence of strong earthquakes.