The Oaxaca, Mexico, earthquake of 1931: lithospheric normal faulting in the subducted Cocos plate
The Oaxaca, Mexico, earthquake of 1931: lithospheric normal faulting in the subducted Cocos plate
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1931 年墨西哥瓦哈卡地震：俯冲科科斯板块中的岩石圈正断层
作者：
S. Singh;G. Suárez;Trinidad Núñez Domínguez
对1931年1月15日发生在墨西哥瓦哈卡的大地震的研究表明，这是一次东西向的正断层地震。震源区1附近缺乏地表断层的证据，体波模型推断震源深度为1040公里，这表明地震发生在俯冲板片内。大规模的地震（Ms = 8.0）强烈表明，破裂突破了整个岩石圈的俯冲科科斯板块。在日本2、阿留申3、秘鲁4和松巴5岛弧中发生的其他大型正断层地震表明，岩石圈断层活动朝向海沟或非常靠近海沟。然而，1931年的地震发生在板块更深的下倾（海沟向陆地方向约150 km），低于似乎是发震板块界面的底部。我们在这里推测，大，虽然不频繁，正断层地震，如1931年的瓦哈卡地震可能有一个作用，在深度去耦俯冲板从板的上部，也许从压倒性的墨西哥大陆板块。1858年米霍坎地震6（Ms 7.5）的震中位置表明，它可能代表了中美洲岛弧岩石圈正断层的另一个例子。这种地震的复发周期不明，对墨西哥的人口中心构成极高的地震风险。
A study of the great earthquake in Oaxaca, Mexico, on 15 January 1931 shows that it was a normal fault earthquake striking east-west. The lack of evidence of surface faulting near the source region1 and the focal depth of ∼40 km inferred from body-wave modelling suggest that the earthquake occurred within the subducted slab. The large size of the earthquake (Ms = 8.0) strongly suggests that the rupture broke through the entire lithosphere of the subducted Cocos plate. Other large, normal fault earthquakes in the Japanese2, Aleutian3, Peruvian4 and Sumba5 arcs show lithospheric faulting seawards of the trench or very close to it. The 1931 event, however, occurred farther down-dip in the slab (∼150 km landward of the trench), below the bottom of what appears to be the seismogenic plate interface. We speculate here that large, although infrequent, normal fault earthquakes such as the 1931 Oaxaca earthquake may have a role in decoupling at depth the subducted slab from the upper part of the slab and perhaps from the overriding Mexican continental plate. The epicentral location of the 1858 Michoacan earthquake6 (Ms≍7.5) suggests that it may represent another example of lithospheric normal faulting in the Middle American arc. Such earthquakes, for which the periods of recurrence are unknown, constitute an extremely high seismic risk to population centres of Mexico.