Mechanism of the 1975 Kalapana, Hawaii, earthquake inferred from tsunami data
Mechanism of the 1975 Kalapana, Hawaii, earthquake inferred from tsunami data
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根据海啸数据推断 1975 年夏威夷卡拉帕纳地震的机制
DOI：
10.1029/1999jb900073
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发表时间：
1999
影响因子：
--
通讯作者：
K. Satake
中科院分区：
文献类型：
--
作者：
K. Ma;H. Kanamori;K. Satake
通过模拟Hilo、Kahului和檀香山三个测潮站观测到的海啸，研究了1975年夏威夷Kalapana地震（M_S= 7.2）的震源机制。我们计算了各种断层模型下的综合海啸。用Ando断层模型（断层长40 km，断层宽20 km，走向N70°E，倾角20°SE，倾角- 90°，断层深度10 km，滑动量5.6 m）计算出的合成海啸到达时间和振幅分别比实际观测结果早10 min，小5倍。试验了不同倾角、不同深度的断层模型。西北倾斜方向的模式比东南倾斜方向的模式产生更大的海啸振幅。断层深度较浅的模型比断层深度较深的模型产生较晚的首次到达。我们还考虑了希利纳断裂系统的影响，但它对海啸激发的贡献微不足道。这表明需要另一种机制来解释海啸。一种可行的模型是沿海岸下沉1米，近海隆起1米的扩展滑塌模型。该模型能较好地解释观测到的海啸的到达时间和振幅。另一种模型是一个更宽的断层模型，它向西北方向倾斜10°，其断层平面延伸到离岸25公里处，远远超出了卡拉帕纳地震的余震区。这两种模式在近海产生了类似的隆升模式，就海啸激发而言，在运动学上是难以区分的。排水量的总量估计为~ 2.5 km^3。通过对滑塌模型和先前地震资料中提出的单力模型的比较，我们认为基拉韦厄火山南侧断裂和大规模滑塌相结合的模型是1975年卡拉帕纳地震最合适的模型。对于基拉韦厄南翼的变形，提出了两种基本的解释机制：(1)岩浆注入引起的裂谷带压力和密度的变化；(2)基拉韦厄南翼陡峭地形造成的重力不稳定。在这两种机制中，南侧翼的大位移都是造成观测到的大海啸的原因。
We investigated the source mechanism of the 1975 Kalapana, Hawaii, earthquake (M_S= 7.2) by modeling the tsunamis observed at three tide-gauge stations, Hilo, Kahului, and Honolulu. We computed synthetic tsunamis for various fault models. The arrival times and the amplitudes of the synthetic tsunamis computed for Ando's fault model (fault length = 40 km, fault width = 20 km, strike = N70°E, dip = 20°SE, rake = −90°, fault depth = 10 km, and slip = 5.6 m) are ∼10 min earlier and 5 times smaller than those of the observed, respectively. We tested fault models with different dip angles and depths. Models with a northwest dip direction yield larger tsunami amplitudes than those with a southeast dip direction. Models with shallower fault depths produce later first arrivals than deeper models. We also considered the effects of the Hilina fault system, but its contribution to tsunami excitation is insignificant. This suggests that another mechanism is required to explain the tsunamis. One plausible model is a propagating slump model with a 1 m subsidence along the coast and a l m uplift offshore. This model can explain the arrival times and the amplitudes of the observed tsunamis satisfactorily. An alternative model is a wider fault model that dips 10°NW, with its fault plane extending 25 km offshore, well beyond the aftershock area of the Kalapana earthquake. These two models produce a similar uplift pattern offshore and, kinematically, are indistinguishable as far as tsunami excitation is concerned. The total volume of displaced water is estimated to be ∼2.5 km^3. From the comparison of slump model and the single-force model suggested earlier from seismological data we prefer a combination of faulting and large-scale slumping on the south flank of Kilauea volcano as the most appropriate model for the 1975 Kalapana earthquake. Two basic mechanisms have been presented for explaining the deformation of the south flank of Kilauea: (1) pressure and density variation along the rift zone caused by magma injection and (2) gravitational instability due to the steep topography of the south flank of Kilauea. In either mechanism, large displacements on the south flank are involved that are responsible for the observed large tsunamis.