新马德里地震带的岩石圈强度与板内形变  

LITHOSPHERIC STRENGTH AND INTRAPLATE DEFORMATION IN THE NEW MADRID SEISMIC ZONE

作　　者：刘澜波[1] MarhD.Zoback 

机构地区：[1]美国康涅狄格大学地质与地球物理系 [2]美国斯坦福大学地球物理系

出　　处：《地球物理学报》1998年第S1期1-14,共14页Chinese Journal of Geophysics

摘　　要：提出一个简单的假说来解释为什么在相对稳定的板块内部地区会存在高地震活动区与高构造形变区．首先，对于大多数板内地区而言，特别是大陆地盾地区与老的海洋盆地，下地壳与上地幔的温度相当低，那里的岩石相对坚硬在这些地区不可能发生明显的岩石圈变形，因为岩石图累积强度大大超过板块驱动力．相反，如果下地壳与上地幔温度相对较高，板块驱动力则主要由上地壳承受，因为下地壳与上地幔相对软弱在这种地区，由于岩石圈累积强度与板块驱动力大小相当，构造形变相对较快．本文将这种假说应用在位于美国中部的新马德里地震带与周围地区．地震带内部热流密度值约为60mw／m2，略高于本区背景热流密度值45mW／m2．计算得到的地温梯度与实验室结果所揭示的延性流动定律表明，在地震带内下地壳与上地幔相当软弱，板内应力主要由上地壳传递．那里的形变速率相对较高．与此相反，在周围地区热流值相对较低，岩石四累积强度大大超过板块驱动力，构造应力由地壳与上地幔共同承受热流值的大小和下地壳上地幔的受力状态是决定地震活动性在地震带内与周围地区强烈对比的主要因素．A simple hypothesis is proposed to explain the occurrence of localized zones of tectonic deformation and seismicity within intraplate regions subjected to relatively uniform far-field tectonic stresses. In moot intraplate regions (especially continental shield areas and old oceanic basins), temperatures in the lower crust and upper mantle are quite low so that the upper mantle is cold and strong. In these regions, significant lithospheric deformation does not occur because the cumulative strength of the lithosphere far exceeds the magnitude of plate-driving forces. If lower crust and upper mantle temperatures are relatively high,however, plate-driving forces are largely supported by the upper crust because the lower crust and upper mantle are relatively weak. In this case, the regions can deform relatively rapidly because the cumulative strength of the lithosphere is compalable in magnitude to that of theforces acting on the lithesphere. In this paper, we apply this hypothesis to the New Madrid seismic zone and the surrounding central and eastern United States. Within the seismic zone,the heat flow appears to be slightly elevated (about 60mW/m2) relative to the background regional value of 45mW/m2. Calculated crustal geotherms and laboratory-derived ductile flow laws suggest that the lower crust and upper mantle are sofficiently weak within the seismic zone that intraplate stresses are largely transmitted through the upper crust and deformation can occur at relatively rapid rates for this intraplate area. In marked contrast, in the surrounding area where the heat flow is relatively low, cumulative lithespheric strength appeals to far exceed the plate-driving force, and the tectonic stress is carried in both the crust and upper mantle. Thus the marked contrast in seismicity betWeen the seismic zone and the surrounding area appeals largely because of heat flow and whether or not the lower crust and upper mantle support an appreciable fraction of the plate-driving forces.

关 键 词：新马德里地震带 形变 应变速率 岩石圈强度 

分 类 号：P315.2[天文地球—地震学]