EPP

On September 8, 2018, an M_S 5.9 earthquake struck Mojiang, a county in Yunnan Province, China. We collect near-field seismic recordings (epicentral distances less than 200 km) to relocate the mainshock and the aftershocks within the first 60 hours to determine the focal mechanism solutions of the mainshock and some of the aftershocks and to invert for the finite-fault model of the mainshock. The focal mechanism solution of the mainshock and the relocation results of the aftershocks constrain the mainshock on a nearly vertical fault plane striking northeast and dipping to the southeast. The inversion of the finite-fault model reveals only a single slip asperity on the fault plane. The major slip is distributed above the initiation point, ~14 km wide along the down-dip direction and ~14 km long along the strike direction, with a maximal slip of ~22 cm at a depth of ~6 km. The focal mechanism solutions of the aftershocks show that most of the aftershocks are of the strike-slip type, a number of them are of the normal-slip type, and only a few of them are of the thrust-slip type. On average, strike-slip is dominant on the fault plane of the mainshock, as the focal mechanism solution of the mainshock suggests, but when examined in detail, slight thrust-slip appears on the southwest of the fault plane while an obvious part of normal-slip appears on the northeast, which is consistent with what the focal mechanism solutions of the aftershocks display. The multiple types of aftershock focal mechanism solutions and the slip details of the mainshock both suggest a complex tectonic setting, stress setting, or both. The intensity contours predicted exhibit a longer axis trending from northeast to southwest and a maximal intensity of Ⅷ around the epicenter and in the northwest.

On Aug. 8, 2017, an M_S7.0 earthquake struck Jiuzhaigou, a county of Sichuan province, China. A number of investigations and studies have been conducted, some of which involved local velocity models. However, the suitability of these models has not been properly addressed. Here we collect 11 already-existing models, including those used in studies of the 2017 M_S7.0 Jiuzhaigou earthquake, choose 10 local stations surrounding the earthquake, and employ the same technique (TRIT) to relocate the hypocenter. And furthermore, we choose a more suitable model from the 11 already-existed models by analyzing the relocation process and the relocated results for reasonability. Finally, our conclusion is that the model Fang2018 is more suitable and the hypocenter parameters, 103.801°E, 33.192°N and 15.8 km for longitude, latitude and depth, respectively, and 2017-08-08 13:19:46.66 for its origin time, based on this model should be recommended for the 2017 M_S7.0 Jiuzhaigou earthquake.