Consistency of Non-Double-Couple Components of Seismic Moment Tensors with Earthquake Magnitude and Mechanism

Abstract

Abstract Earthquake moment tensors can be decomposed into double-couple components describing slip on planar faults and non-double-couple (NDC) components. NDC components can arise in three ways. Some appear to be intrinsic, indicating complex source processes differing from slip on a fault for earthquakes in specific geologic environments, notably volcanic areas. Others are additive, reflecting the combined effect of double-couple sources on multiple faults with different geometries. Alternatively, they may be artifactual, results of the inversion without geologic meaning. Combining moment tensors from three global and four regional catalogs for 2016–2020 provides a dataset of NDC components of 12,856 earthquakes with 2.9<Mw<8.2 in various geologic environments. The distributions of NDC components vary only slightly with magnitude, with a mean deviation from a double-couple source of around 20%. The consistency suggests that most NDC components do not reflect rupture on multiple faults, which is expected only for larger earthquakes. Similarly, there are only small differences in NDC components between earthquakes with different faulting mechanisms or in different geologic environments. These consistencies suggest that most NDC components are not intrinsic due to complex source processes that are often assumed to be most likely in volcanic and thus extensional areas. Hence, it appears that for most earthquakes, especially smaller ones, the NDC components are largely artifacts of the inversion.