Increased long‐range intermediate‐magnitude earthquake activity prior to strong earthquakes in California
Increased long‐range intermediate‐magnitude earthquake activity prior to strong earthquakes in California
复制标题
DOI：
10.1029/95jb03730
复制
发表时间：
1996-03
影响因子：
--
通讯作者：
L. Knopoff;T. Levshina;V. Keilis-Borok;C. Mattoni
中科院分区：
文献类型：
--
作者：
L. Knopoff;T. Levshina;V. Keilis-Borok;C. Mattoni
我们研究了加利福尼亚州的强地震与其前后的中级地震之间的时空关系。 1941年至1993年间，加利福尼亚州发生的所有11次名义震级大于或等于6.8级的地震之前，震级大于或等于5.1级的地震发生率均有所增加。 11 次地震中有 10 次发生在中等震级活动大于 75% 时或之后不久。其中 3 次强震与 11 场强震中的其他震级具有传统的时空前震余震关系。前兆活动集中在线性尺寸为数百公里量级的区域；这些尺寸明显大于随后发生的强地震的估计断裂长度。对于较小的地震，相关性不明确；对于震级小于 4.6 级的地震，相关性几乎无法识别。强震的前兆出现的时间间隔约为强震前 5 至 10 年，尽管强震发生的时间大约比旧金山地震早 25 年。就洛马普列塔地震和旧金山地震而言，活动增加的开始似乎相对突然。增加的活动要么在强地震发生后不久突然停止到数百公里量级的距离，要么强事件本身就是在随后不久发生的第二次强地震之前持续高活动的前兆模式的一部分，随后活动随之消失。因此，中震前兆并不直接影响后续强震发生的时间和地点，但强震对中震附近至强震震级数倍量级的应力场有较强的影响。
We study the space-time relationships between strong earthquakes in California and the intermediate-magnitude earthquakes that both precede and follow them. All 11 earthquakes in California with nominal magnitudes greater than or equal to 6.8 from 1941 to 1993 were preceded by an increase in the rate of occurrence of earthquakes having magnitudes greater than 5.1. Ten of the 11 earthquakes occurred when or shortly after the intermediate magnitude activity was greater than its 75th percentile. Three of these strong earthquakes are in a conventional space-time foreshock-aftershock relationship with others of the 11 strong events. The precursory activity is concentrated in regions having linear dimensions of the order of a few hundred kilometers; these dimensions are significantly larger than the estimated fracture lengths of the ensuing strong earthquakes. The correlations are ill defined for smaller earthquakes and are almost unidentifiable for earthquakes with magnitudes less than about 4.6. The precursors to the strong earthquakes appear over a time interval of the order of 5 to 10 years before the strong earthquake, although the onset was about 25 years before the San Francisco earthquake. In the case of the Loma Prieta and San Francisco earthquakes, the onset of increased activity appears to be relatively abrupt. The increased activity is either switched off abruptly to distances of the order of hundreds of kilometers shortly after the occurrence of a strong earthquake, or the strong events are themselves part of a precursory pattern of continuing high activity before a second strong earthquake that takes place soon thereafter, with subsequent extinction of activity after it. Thus the intermediate-magnitude precursors do not directly influence the time and location of the subsequent strong event, but the strong event has a strong influence on the stress field in the vicinity of intermediate-magnitude earthquakes to distances of the order of many times the scale size of the strong earthquake.