Multi-array Back-projection with a 3-D Global Tomography Model: Case Study of the 2017 Mw7.7 Russia Earthquake

Imaging the rupture process with back-projection (BP) method is widely used today to investigate devastating earthquakes on subduction zones. In order to avoid error induced by velocity structure variation along the ray path with 1-D layered homogeneous model, we use a global 3-D P-wave tomography model, the LLNL-G3Dv3 model, to compute travel time and carry out BP with multi-array data. We apply this method to the newly happened July 17, 2017 Mww7.7 Russia Earthquake, whose location is (54.4715°N, 168.8148°E) and source depth is 10.99 km. We obtain preliminary BP results with data of Europe (EU) and North America (NA) from IRIS. The NA result shows this earthquake has a unilateral rupture propagation towards southeast direction with 123°. It ruptured a length of 174km with a speed of 2.9 km/s. The EU result shows similar rupture direction with 120°. However, the length and speed are much smaller, which are 120 km and 1.3 km/s. Based on data quality and BP results, characteristics revealed by NA are more convincing. The earthquake is located at the western region of Aleutian arc, which marks the zone where the Pacific Plate subducts into the mantle beneath the North American Plate. This portion is characterized by transform motion between the two plates, along with weak volcanism, no large events in record. Moreover, relatively large events (M5-6) here generally are shallow, mostly strike-slip, and this earthquake is quite an example except its magnitude. The BP results inferred by both NA and EU show a common feature that rupture propagate just along the strike of the slab zone, which could also demonstrate the validity of our results.