Lg Attenuation near the North Korean Border with China, Part I: Model Development from Regional Earthquake Sources

摘要

We have collected broadband data from three seismic networks-two portable and one permanent-in a remote part of northeast China bordering North Korea. The combined network coverage allows first-hand investigations of seismic-wave propagation in a region of import for nuclear test ban monitoring research. Application of the reversed two-station method to the newly acquired data has produced stable measurements of the quality factor Q (= Q(0)f(eta)) for Lg waves. The results, a weighted regional average over 23 interstation paths involving 51 events and 21 stations, point to 1 Hz Q (or Q(0)) of 345 and eta of 0.38 in a jarring incongruity with what appears to be a popular perception of the region as being of very low attenuation for Lg waves. The results also show that Lg Q varies from one interstation path to another. The highest Lg-wave attenuation (110 < Q(0) < 140) is found along interstation paths that crossed two recently active volcanoes (Huangyishan and Changbaishan). The subregion exhibiting the next highest Lg attenuation is Bohai, an extensional basin known to feature above- average heat flow.