A strong earthquake with magnitude M_W=7.1 occurred in the area of Molucca Sea, Indonesia on November 14, 2019(Coordinated Universal Time, UTC), and then generated a small-scale local tsunami. In order to better understand the earthquake source characteristics and seismogenic structure, as well as to assess the hazard of tsunami caused by earthquake, this paper mainly focuses on the regional tectonic background, the focal mechanism, and tsunami numerical simulation for the Molucca Sea M_W7.1 earthquake. The broadband seismic waveforms from IRIS Data Management Center are used to estimate the moment tensor solution of this earthquake by W phase method. The result shows that the Molucca Sea earthquake occurred at a shallow depth on a high dip-angle, right-lateral reverse fault, the aftershocks were distributed along the SSW-NNE direction and concentrated near the main shock. These results indicate the Molucca Sea earthquake with characteristic of compressional rupture occurred in the complex plate boundary region of eastern Indonesia, which is dominated mostly by the collision interaction of the Halmahera slab and the Sangihe slab in the east and west sides of Molucca Sea under control of current regional stress field. The coseismic displacements of Molucca Sea M_W7.1 earthquake calculated using Okada's model of rectangular dislocation in a uniform elastic half-space show that the Molucca Sea earthquake generated vertical coseismic deformation with a maximum uplift of 0.15m when the rupture occurred along the high dip-angle reverse fault. The synthetic tsunami waveforms are provided by COMCOT tsunami modelling package solving the nonlinear shallow water wave equations based on the determined fault geometry from W phase inversion. These studies indicate the vertical coseismic deformation resulting in the sudden uplift of water volume above the earthquake source, and finally inducing a small-scale local tsunami. The energy of tsunami mainly propagates to both side of the fault, and part of energy propagates to Sula Islands of Indonesia along the fault dislocation direction; and compared with the first cycle of tsunami records observed by tide gauges deployed along the coastal line of earthquake source region, the observed tsunami head wave fits well with the synthetic wave, both are consistent in amplitude and tsunami arrival time, but the follow-up waveforms are quite different. The numerical simulation of tsunami shows that, in combination with the fault geometry parameters obtained by W phase fast inversion, the tsunami numerical model can be used for tsunami early warning, and it provides sufficient accuracy for forecasting tsunami wave height, thus, having great practical significance for understanding the propagation process and disaster distribution of tsunami.

A magnitude M_W7.0 earthquake struck north of Anchorage, Alaska, USA on 1 December 2018. This earthquake occurred in the Alaska-Aleutian subduction zone, on a fault within the subducting Pacific slab rather than on the shallower boundary between the Pacific and North American plates. In order to better understand the earthquake source characteristics and slip distribution of source rupture process as well as to explore the effect of tectonic environment on dynamic triggering of earthquake, the faulting geometry, slip distribution, seismic moment, source time function are estimated from broadband waveforms downloaded from IRIS Data Management Center. We use the regional broadband waveforms to infer the source parameters with ISOLA package and the teleseismic body wave recorded by stations of the Global Seismic Network is employed to conduct slip distribution inversion with iterative deconvolution method. The focal mechanism solution indicates that the Alaska earthquake occurred as the result of tensile-type normal faulting, the estimated centroid depth from waveform inversion shows that the earthquake occurred at the depth of 56.5km, and the centroid location is 10km far away in northeast direction relative to the location of initial epicenter. We use the aftershock distribution to constrain the fault-plane strike of a normal fault to set up the finite fault model, the finite fault inversion shows that the earthquake slip distribution is concentrated mainly on a rectangular area with 30km×20km, and the maximum slip is up to 3.6m. In addition, the slip distribution shows an asymmetrical distribution and the range of possible rupture direction, the direction of rupture extends to the northeast direction, which is same as that of aftershock distribution for a period of ten days after the mainshock. It is interesting to note that a seismic gap appears in the southwest of the seismogenic fault, we initially determined that the earthquake was a typical normal fault-type earthquake that occurred in the back-arc extensional environment of the subduction collision zone between the Pacific plate and the North American plate, this earthquake was not related to tectonic movement of faults near the Earth's surface. Due to the influence of high temperature and pressure during the subduction of the Pacific plate toward to the north, the subduction angle of the Pacific plate becomes steep, causing consequently the backward bending deformation, thus forming to a tensile environment at the trailing edge of the collision zone and generating the M_W7.0 earthquake in Alaska.