The Rudbar-Tarom earthquake of 20 June 1990 in NW Persia: Preliminary field and seismological observations, and its tectonic significance
The Rudbar-Tarom earthquake of 20 June 1990 in NW Persia: Preliminary field and seismological observations, and its tectonic significance
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1990 年 6 月 20 日波斯西北部鲁德巴尔-塔罗姆地震：初步现场和地震观测及其构造意义
DOI：
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发表时间：
1992
影响因子：
3
通讯作者：
T. Wallace
中科院分区：
文献类型：
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作者：
M. Berberian;M. Qorashi;J. Jackson;K. Priestley;T. Wallace
1990年6月20日波斯西北部鲁德巴尔-塔罗姆地震（M S 7.7，m B 6.4，M W 7.3）造成约4万人死亡，50多万人无家可归，摧毁了三个城市（Rudbar、Manjil和Lowshan）和700个村庄，另有300个村庄受到轻微破坏，里海西南部。在震中区观察到与地震有关的断层和褶皱。同震地表断层至少与三个主要的不连续的复杂断层段有关，总长度超过80公里。这三个主要的断层段被安排在一个右阶雁列模式，并在所观察到的表面破裂的间隙分开。每一段的走向为95°至120°，在接近垂直的断层或向南或SSW倾斜的断层上有斜向左旋和反向运动。最大地表位移水平（左侧）为60厘米，垂直（南侧向上）为95厘米。地震后在地表也观察到反向或逆冲意义上的层面滑动，可能发生在同震褶皱期间。主震的地震体波证实了断层的左旋性质，并表明在三个主要的子事件中发生了滑动，这些子事件可能对应于在地表看到的断层段。从宽带体波得到的震源机制几乎是纯粹的走滑，几乎没有证据表明在表面看到的运动的垂直分量。有许多余震，其中一个具有逆冲断层机制，不同于主震。鲁德巴尔-塔罗姆地震发生的复杂地表断层系统以前没有被确定为活跃的。在1990年移动的断层上没有明显的第四纪陡坎，这表明这类地震的重现期相对较长;但这很难量化，因为侵蚀率很高。虽然波斯地震台网的覆盖范围不足以精确定位小地震，以确定活动断层，但该地区有许多现代和历史地震活动，以及快速活动构造过程的丰富地貌证据。以往对震源机制和活动断裂的研究强调了逆断层和褶皱作用，而逆断层和褶皱作用无疑是形成阿尔博尔兹山带的主要过程。1990年的地震提供了第一个证据，表明该带也经历了左旋剪切。在阿尔博尔茨山南缘，地震滑动方向近似为NE，发生在斜断层上。我们怀疑，在高Alborz，那里的缩短量和地形更大，波斯和里海南部之间的斜向收敛被分割成基本上纯粹的反向运动和左旋走滑。
Abstract The Rudbar-Tarom earthquake of 20 June 1990 in NW Persia ( M S 7.7, m b 6.4, M W 7.3) killed approximately 40,000 people, left more than 500,000 homeless, destroyed three cities (Rudbar, Manjil, and Lowshan) and 700 villages, and slightly damaged another 300 villages, in the densely populated area of the western Alborz mountains, southwest of the Caspian Sea. Both faulting and folding associated with the earthquake were observed in the epicentral area. Co-seismic surface faulting was associated with at least three main discontinuous, complex fault segments with a total length of more than 80 km. These three main fault segments are arranged in a right-stepping en-echelon pattern and are separated by gaps in the observed surface ruptures. Each segment has a strike of 95° to 120°, with oblique left-lateral and reverse motion on faults that are subvertical or have steep dips to the S or SSW. Maximum surface displacements were 60 cm horizontal (left lateral) and 95 cm vertical (south side up). Bedding-plane slip in a reverse or thrust sense was also observed at the surface following the earthquake and may have occurred during co-seismic folding. Seismic body waves of the mainshock confirm the left-lateral nature of the faulting and show that slip occurred in three main subevents that may correspond to the fault segments seen at the surface. The focal mechanism obtained from broadband body waves is almost pure strike slip, with little evidence of the vertical component of motion seen at the surface. There were numerous aftershocks, one of which had a thrust faulting mechanism, different from that of the mainshock. The complex system of surface faults on which the Rudbar-Tarom earthquake occurred had not previously been identified as active. The lack of obvious Quaternary scarps on the faults that moved in 1990 suggests that return periods for earthquakes of this type are relatively long; but this is difficult to quantify, as erosion rates are high. Although the Persian seismic network has insufficient coverage to locate small earthquakes with enough precision to identify active faults, there is much modern and historical seismicity in the area, and abundant geomorphological evidence of rapid active tectonic processes. Previous studies of focal mechanisms and active faulting had emphasized the reverse faulting and folding that are undoubtedly the main processes that build the Alborz mountain belt. The 1990 earthquake provided the first evidence that the belt also undergoes left-lateral shear. On the southern edge of the Alborz mountains the slip direction in earthquakes is approximately NE and occurs on oblique faults. We suspect that in the high Alborz, where the amount of shortening and the topography are greater, this oblique convergence between Persia and the southern Caspian Sea is partitioned into essentially pure reverse motion and left-lateral strike-slip.