A NEW CONSTRAINT ON THE COMPOSITION OF THE TOPMOST CONTINENTAL MANTLE - ANOMALOUSLY DIFFERENT DEPTH INCREASES OF P-VELOCITY AND S-VELOCITY

被引：13

作者：

GAJEWSKI, D ^{[1
]}

STANGL, R ^{[1
]}

FUCHS, K ^{[1
]}

SANDMEIER, KJ ^{[1
]}

机构：

[1] UNIV KARLSRUHE,INST GEOPHYS,W-7500 KARLSRUHE 21,GERMANY

来源：

GEOPHYSICAL JOURNAL INTERNATIONAL | 1990年 / 103卷 / 02期

关键词：

S[!sub]n[!/sub] amplitudes; topmost continental mantle; V[!sub] P [!/sub]/V[!sub]S[!/sub] ratio;

D O I：

10.1111/j.1365-246X.1990.tb01787.x

中图分类号：

P3 [地球物理学]; P59 [地球化学];

学科分类号：

0708 ; 070902 ;

摘要：

Compared to clear crustal P‐ and S‐waves as well as a strong refracted Pn‐wave propagating in the topmost mantle (i.e., 10 to 15 km below the Moho), an anomalously weak appearance of the corresponding refracted shear wave Sn is observed on refraction seismic profiles in SW Germany, France, coastal Maine (NE United States) and Fennoscandia. It is possible that the observation of Pn/PMP ratios close to unity combined with small Sn/SMS ratios (i.e., small Sn amplitudes) is typical for the continental uppermost mantle since this was observed for quite different types of continental crust. It is shown that the observed phenomenon is not a source effect. Several possible causes to explain the observations are studied, also with the aid of synthetic seismograms. The effects of temperature, attentuation and anisotropy have been investigated. Their influence cannot explain the observations. The most likely candidate is a depth‐increasing VP/VS ratio (an increase in the order of 0.027 over a depth range of 10 km), forcing P‐ and S‐waves to propagate on different paths in the topmost mantle. The observed phenomenon provides new constraints on the change of composition with depth for the crust mantle transition zone with basalt depletion as the most likely explanation. Copyright © 1990, Wiley Blackwell. All rights reserved

引用

页码：497 / 507

页数：11

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