On variations of heat flow and Pn velocity— A case study from the continental area of China

Abstract

Temperature is an important factor affecting seismic velocity, and terrestrial heat flow is the direct indication of the thermal state of the lithosphere. Some authors suggested that Pn velocity was closely related with heat flow. Average heat flow values ( q) and Pn velocities ( V Pn) from 22 regions have been calculated and collected from published literature to investigate the possible correlationship between these two parameters for the continental area of China. The regional average heat flow values vary from 43 to 99 mW m −2, corresponding to a Pn velocity range of 7.6–8.4 km s −1. Results show that the variations of q and V pn are far away from any significant inverse relation. Dependencies of seismic velocity on pressure and heat flow on crustal radiogenic heat have been taken into consideration in regressions. However, all the corrections are of little help for the improvement of the expected inverse relation. Various interpretations have been discussed. Seismic velocity is a function of multi varieties. At the depth of Moho boundary, it can at most be simplified as a function of pressure and temperature. With respect to depth, effects of geopressure and geotemperature on V pn are of exactly the same order with opposite sign. Therefore, any meaningful q- V pn relationship should be sensitive to the correction of pressure effect on V pn. But even the relation for the North America (Black and Braile, 1982) is dull of pressure correction. The conclusion deduced from the present study is that temperature at the Moho boundary is not the most important factor affecting Pn velocity. The conceptual inverse correlationship between heat flow and Pn velocity might be masked by various “noises”. The non-inverse correlationship has been interpreted as a result of the complex deep structure, unnegligible heterogeneity of the upper mantle and the thermal processes at depth of the lithosphere in the continental area of China.