Depth Dependence of Source Characteristics of Slow-Slip Events and Earthquakes on Thrust Faults

Abstract:

Earthquakes and slow-slip events (SSEs) partially relieve the elastic strain that slowly builds up at the boundary of tectonic plates. The strain drop is a common parameter to both types of events that is fundamental to describe the amount of fault slip, surface displacements and also helps predict rupture size in a seismogenic zone. Strain drop seems to be relatively uniform over a wide range of earthquake magnitudes. However, its variation among different types of events, seismic and aseismic is poorly understood. Here, we build a comprehensive catalogue of earthquakes and SSEs to show that strain drop decides the style of rupture. On average, SSEs have strain drops 1 to 2 orders of magnitude lower than earthquakes, indiscriminate of tectonic context. Strain drop seems to decrease with depth, with tsunami earthquakes having the largest strain drop. Shallow, continental, earthquake have larger strain drop than typical subduction zone earthquakes, implying rupture mechanism varying with depth. Strain drop between events that occur in different regions show no trends with their moment magnitude. However, for SSEs that rupture the same area, the strain drop varies directly with moment magnitude. By combing all the above observations we see that many physical parameters, shows strong depth dependence, indicating depth-dependent segmentation of the seismogenic zone in megathrusts. This, along with a geometry of an existing seismic gap can help predict the hazard associated when that region relieves strain.