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1929年大浅滩地震(M_s=7.2)是发生在加拿大的最大和最致命的地震之一。这次地震引起的海啸和海底滑坡造成大量的死亡和破坏。曾经认为(Hasegawa and Kanamori,1987),单力机制(滑坡)比双力偶机制更符合观测资料,因之曾认为这个事件不是地震。但是个别的研究只考虑了4个双力偶解并且留下了许多不能回答的问题,特别是与震源时间函数和沉积物体积有关的问题。本文用了大量的地震图来核查全范围的双力偶解,以便进一步确定这次事件的性质。通过波形正演和反演两种方法,表明这是一次有复杂震源机制的地震事件。第1个也是最大约子事件是沿北西走向断层面发生的走滑双力偶事件,后面两个子事件可能是沿北东走向断层面上的走滑双力偶机制,但也不能完全排除其他类型的机制。第1个子事件有约束较好、为20±2km的震源深度,另两个子事件深度似乎也为20km,但精度为±5km。这些震源深度结果也说明这次事件不是滑坡。子事件地震矩之和相当于一个M_w=7.2±0.3的地震,和长周期资料的矩心矩张量(CMT)方法得到的M_w=7.1±0.1的地震的矩很一致,也和直接从地震图上计算的M_s=7.2(±0.3),m_b=7.1(±0.2)的矩差不多。用双力偶机制模拟海底位移结果表明,海啸是滑坡产生的,不是地震直接引起的。
The 1929 Grand Shoal Earthquake (M_s = 7.2) was one of the largest and deadliest earthquakes in Canada. The tsunami caused by the earthquake and the seabed landslide caused a great deal of death and destruction. It has been considered (Hasegawa and Kanamori, 1987) that the single-force mechanism (landslide) is more in line with the observed data than the dual-couple mechanism, which was not considered an earthquake. However, individual studies considered only four double couple solutions and left many unanswerable questions, especially problems related to source time functions and sediment volumes. In this paper, a large number of seismograms are used to verify the full range of dual couple solutions to further determine the nature of the incident. Through forward wave and inversion methods, it shows that this is a seismic event with complex focal mechanism. The first and greatest causation event is a strike-slip dual-couple event along the northwesterly fault plane. The latter two sub-events may be strike-slip dual-couple mechanisms along the north-east strike fault plane, but other types of mechanism. The first sub-event is well-constrained, with a focal depth of 20 ± 2 km. The depths of the other two sub-events also appear to be 20 km, but the accuracy is ± 5 km. The depth of these hypocenters also shows that this incident is not a landslide. The sum of the sub-event seismic moments is equivalent to an earthquake with M_w = 7.2 ± 0.3. It is consistent with the M_w = 7.1 ± 0.1 earthquake moment obtained from the long-period CMT method and also directly from the earthquake The calculated moment of M_s = 7.2 (± 0.3), m_b = 7.1 (± 0.2) is almost the same. The simulation of the displacement of the seafloor by the dual couple mechanism shows that the tsunami is caused by the landslide and not directly caused by the earthquake.