10:45 AM - 12:15 PM
[STT43-P05] Seismic source inversion using high degree-of-freedom models
Keywords:Seismic source inversion, high degree-of-freedom models, 2022 Taitung, Taiwan, earthquake
One method for estimating the rupture propagation process of a fault is the finite-fault inversion method, which can estimate the spatio-temporal distribution of slip-rate on the fault plane. When using this method, some constraints are introduced to solve the problem stably, as the amount of information in the data is not sufficient. Constraints include well-known ones such as smoothing and sub-fault dimensions, as well as others that limit the model space, such as setting the duration at which a fault can rupture. While the former is widely recognized and various studies have been conducted, the model space restriction by the latter has not been sufficiently examined for its appropriateness. In addition, in finite fault inversion, setting a shorter duration of possible slip on the fault tends to make it easier to select a solution with less smoothing. In other words, it is more favorable to restrict the model space in order to obtain detailed solutions. As a result, many finite fault inversion methods have been developed in the direction of restricting the model space in order to obtain detailed solutions. However, if the model space is not properly set up, the solutions obtained will be distorted.
The Potency Density Tensor Inversion (PDTI) have been developed in the direction of increasing the degree of freedom of the model by extending the prescribed double-couple representing fault slip from 2 to 5. Numerical experiments and applications to real earthquakes have shown that PDTI can stably analyze earthquakes with complex seismic source processes and that information on fault geometry can be inferred from the data. On the other hand, although it has not been discussed extensively, modelling has been used in PDTI-based analyses that allows flipping of the direction of rupture propagation. The idea behind such modelling has been to extract as much information as possible from the data without distorting it, rather than to obtain a detailed solution that is distorted by restricting the model space. As a result, many earthquakes with flipped rupture propagation directions have been found in analyses using high degree-of-freedom models. The flipped direction of rupture propagation revealed by PDTI can also be confirmed by other independent data. For example, in the 2022 Taitung, Taiwan, earthquake, PDTI revealed that the direction of rupture propagation flipped during the main shock, and similar results can be obtained from strong-motion observation records along the fault. In this presentation, a new direction in seismic source process analysis, "appropriately increasing the degree-of-freedom of the model", is presented and its implications are discussed.
The Potency Density Tensor Inversion (PDTI) have been developed in the direction of increasing the degree of freedom of the model by extending the prescribed double-couple representing fault slip from 2 to 5. Numerical experiments and applications to real earthquakes have shown that PDTI can stably analyze earthquakes with complex seismic source processes and that information on fault geometry can be inferred from the data. On the other hand, although it has not been discussed extensively, modelling has been used in PDTI-based analyses that allows flipping of the direction of rupture propagation. The idea behind such modelling has been to extract as much information as possible from the data without distorting it, rather than to obtain a detailed solution that is distorted by restricting the model space. As a result, many earthquakes with flipped rupture propagation directions have been found in analyses using high degree-of-freedom models. The flipped direction of rupture propagation revealed by PDTI can also be confirmed by other independent data. For example, in the 2022 Taitung, Taiwan, earthquake, PDTI revealed that the direction of rupture propagation flipped during the main shock, and similar results can be obtained from strong-motion observation records along the fault. In this presentation, a new direction in seismic source process analysis, "appropriately increasing the degree-of-freedom of the model", is presented and its implications are discussed.