A thinned lithospheric image of the Tanlu Fault Zone, eastern China: Constructed from wave equation based receiver function migration

Abstract

We apply the newly proposed wave equation‐based receiver function poststack migration method to the Northern China Interior Structure Project broadband data to image the lithospheric structure of the Tanlu Fault Zone area in eastern China. Our migration result reveals a 60‐ to 80‐km‐thick present‐day lithosphere beneath the study region, significantly thinned from the Paleozoic lithosphere of >180 km. The lithosphere‐asthenosphere boundary (LAB) is coherently imaged along the ∼300‐km east‐west profile, displaying an arc‐like shape with its apex roughly coincident with the transverse location of the Tanlu Fault Zone on the surface. An obvious uplift from ∼36 km to ∼32 km of the Moho is also clearly detected right below this fault zone. The coincidence of the imaged Moho uplift and the LAB apex with the surface location of the Tanlu Fault Zone provides seismological evidence for the steep geometry and deep penetration of the fault system, and indicates that the Tanlu Fault Zone might have acted as a major channel for anthenosphere upwelling during the Mesozoic‐Cenozoic continental extension and lithospheric thinning in eastern China. Frequency analysis and synthetic modeling suggest that both the Moho and the LAB are sharp and strong. The latter, in particular, is constrained to have a 3–7% drop in S wave velocity over a depth range of 10 km or less. Such a rapid velocity change at the base of the lithosphere in the study region cannot be solely explained by thermal variation, but likely reflects the presence of volatiles or melt in the asthenosphere, or is partially attributed to the compositional contrast between the preserved depleted and dehydrated cratonic lithospheric veneer and the uplifted hydrated and fertile asthenospheric materials.