Geologic Setting, Field Survey and Modeling of the Chimbote, Northern Peru, Tsunami of 21 February 1996
Geologic Setting, Field Survey and Modeling of the Chimbote, Northern Peru, Tsunami of 21 February 1996
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1996 年 2 月 21 日秘鲁北部钦博特海啸的地质背景、实地调查和建模
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发表时间：
1999
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通讯作者：
E. Norabuena
中科院分区：
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作者：
J. Bourgeois;C. Petroff;H. Yeh;V. Titov;C. Synolakis;Boyd C. Benson;J. Kuroiwa;J. Lander;E. Norabuena
秘鲁10°S以南的海岸历史上经常发生海啸性地震，而10°S以北的俯冲带则相对平静。在1996年2月21日格林尼治时间21:51（当地时间07:51），一场大的海啸性地震（哈佛估计Mw = 7.5）袭击了9.6°S, 79.6°W，距离秘鲁北部海岸约130公里，Mendaña断裂带与秘鲁-智利海沟相交的北部。从地震资料推断，可能的机制是低角度逆冲，与纳斯卡板块在南美板块下的俯冲一致，具有相对缓慢的破裂特征。主震发生大约一小时后，一场破坏性的海啸袭击了秘鲁海岸，造成12人死亡。我们报告了在7.7°S至11°S范围内的调查测量结果，包括最大上升（2-5m， 8 - 10°S之间）、最大淹没距离（超过500米）和海啸沉积物沉积模式。观测和数值模拟表明，这次事件的水动力特征与1992年尼加拉瓜海啸相似。气候、植被和人口的差异使这两次海啸看起来比实际情况更不一样。1996年的钦博特地震是秘鲁自17世纪以来第一次发生在8 - 10°S之间的俯冲带（板块间）大地震（Mw bb0.7），与1960年发生在6.8°S的地震（Mw 7.6）相似。这两个事件显然是自1619年以来秘鲁北部唯一的大俯冲带地震（东经8°S，东经7.8毫瓦）；这两次海啸造成的死亡人数也都超过了18世纪以来秘鲁发生的任何一次海啸。我们同意Pelayo和Wiens（1990,1992）的观点，即秘鲁北部的这个俯冲带与其他俯冲带相似，这些俯冲带只是弱耦合的，收敛在很大程度上是地震性的。当俯冲带地震发生时，它们是缓慢的，通常是浅层的，并且起源于远离海岸的地方（靠近楔尖）。因此，震感很弱，当地居民也没有预料到随之而来的海啸。虽然钦博特海啸可能是一个边缘案例，但它显然是另一个“海啸地震”的唤醒例子。
Abstract—Whereas the coast of Peru south of 10°S is historically accustomed to tsunamigenic earthquakes, the subduction zone north of 10°S has been relatively quiet. On 21 February 1996 at 21:51 GMT (07:51 local time) a large, tsunamigenic earthquake (Harvard estimate Mw = 7.5) struck at 9.6°S, 79.6°W, approximately 130 km off the northern coast of Peru, north of the intersection of the Mendaña fracture zone with the Peru–Chile trench. The likely mechanism inferred from seismic data is a low-angle thrust consistent with subduction of the Nazca Plate beneath the South American plate, with relatively slow rupture characteristics. Approximately one hour after the main shock, a damaging tsunami reached the Peruvian coast, resulting in twelve deaths. We report survey measurements, from 7.7°S to 11°S, on maximum runup (2–5m, between 8 and 10°S), maximum inundation distances, which exceeded 500 m, and tsunami sediment deposition patterns. Observations and numerical simulations show that the hydrodynamic characteristics of this event resemble those of the 1992 Nicaragua tsunami. Differences in climate, vegetation and population make these two tsunamis seem more different than they were. This 1996 Chimbote event was the first large (Mw>7) subduction-zone (interplate) earthquake between about 8 and 10°S, in Peru, since the 17th century, and bears resemblance to the 1960 (Mw 7.6) event at 6.8°S. Together these two events are apparently the only large subduction-zone earthquakes in northern Peru since 1619 (est. latitude 8°S, est. Mw 7.8); these two tsunamis also each produced more fatalities than any other tsunami in Peru since the 18th century. We concur with Pelayo and Wiens (1990, 1992) that this subduction zone, in northern Peru, resembles others where the subduction zone is only weakly coupled, and convergence is largely aseismic. Subduction-zone earthquakes, when they occur, are slow, commonly shallow, and originate far from shore (near the tip of the wedge). Thus they are weakly felt, and the ensuing tsunamis are unanticipated by local populations. Although perhaps a borderline case, the Chimbote tsunami clearly is another wake-up example of a "tsunami earthquake."