The depths of the deepest deep earthquakes
The depths of the deepest deep earthquakes
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最深地震的深度
DOI：
10.1029/jb090ib02p01859
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发表时间：
1985
影响因子：
--
通讯作者：
C. Frohlich
中科院分区：
文献类型：
--
作者：
P. Stark;C. Frohlich
地震活动的最大深度是对地幔动力学模型提供约束的基本观测。虽然最近对地幔地震活动和动力学的研究表明，地震活动延伸到“大约700公里”，但据报道，大地震的震源深度为720公里，小地震的震源深度超过800公里。我们研究了几个星表中的事件的震源深度，得出结论：（1）最深的可靠震源深度约为670-680 km，而震源深度低于600 km的事件发生在几个相距甚远的地理区域;（2）支持震源深度超过680 km的观测通常很少、很差或不一致，（3）650 km以下地震活动减弱是相当突然的。然而，我们不能确定活动是否在670-680 km处完全停止，或者事件的最大规模在650 km以下逐渐减小，偶尔在650 km处出现6.5-7.0级，在680 km处出现5.5-6.0级，在695 km处出现4.0-4.5级等。有两种模型与在相距很远的地区，在大约650-680公里处突然终止活动是一致的：一种阻挡俯冲岩石圈穿透的屏障，或一种在俯冲物质进入下地幔时改变其性质的相变。
The maximum depth of seismic activity is a fundamental observation providing a constraint on models of mantle dynamics. Although most recent investigations of mantle seismicity and dynamics state that seismicity extends to “about 700 km,” focal depths of 720 km have been reported for large earthquakes, as well as depths greater than 800 km for small events. We have examined focal depths of events in several catalogs and conclude that (1) the deepest reliable focal depths are at about 670–680 km, and events with focal depths beneath 600 km occur in several widely separated geographic regions, (2) observations supporting focal depths exceeding 680 km are usually few, poor, or inconsistent, (3) the reduction of seismic activity beneath about 650 km is quite abrupt. However, we cannot determine whether activity stops completely at 670–680 km, or the maximum size of events decreases gradually beneath 650 km, with magnitudes of 6.5–7.0 occasionally occurring at 650 km, magnitudes of 5.5–6.0 at 680 km, 4.0–4.5 at 695 km, etc. Several models can explain the absence of seismic activity in the lower mantle. Two models are consistent with the abrupt termination of activity at about 650–680 km in widely separated areas: a barrier which resists penetration by the subducting lithosphere or a phase transition which modifies the properties of the subducted material as it goes into the lower mantle.