Characterizing the 2013 Songyuan Earthquake Sequence in Central Songliao Basin, Northeast China

Abstract:

In a period of about 1 month starting on October 31, 2013, the Songyuan region inside the central Songliao Basin, northeast China, characterized by null or low historical seismicity, was severely shaken by an intense earthquake sequence, causing significant casualties and property damage. The unusual earthquake sequence included two seismic swarm episodes. At 03:03 UTC on October 31, 2013, the first episode started with an earthquake of Ms 5.7, followed by an Ms 5.1 earthquake. 23 days later, on November 23, another Ms 5.8 earthquake hit the same area. It was preceded by an Ms 5.2 foreshock and followed by an Ms 5.0 aftershock. In addition to these five magnitude 5+ earthquakes, more than 200 aftershocks with a local magnitude scale of ≥1.0 were also recorded. Immediately after the first Ms 5.7 shock, a temporary seismic network of 7 short period stations were deployed in the source area. The combined dataset from permanent and temporary arrays provide us an excellent opportunity to investigate the dynamics of this earthquake sequence. In this study, we first inverted the complete moment tensor of the 5 largest events (Ms > 5) using the combined waveform data. The focal mechanism solutions suggest that the 5 events are predominant by high-angle reverse faulting with an NNE-SSW orientation. The P axis aligns horizontally in the W-E direction, consistent with the regional stress field of the area. In addition, the inverted moment tensor also appears to have significant amount of non-DC component, which might be related to water injection and hydraulic fracturing activities for enhancing oil/gas recovery in the area. By applying double-difference relocation and template based matching technique, we plan to delineate the spatiotemporal evolution of the seismic swarm. Our ultimate goal is to have a better understating of the seismotectonic structure of the fault system and to further explore potential physical processes (stress, fluids etc.) that are responsible for this unusual earthquake sequence.