Yun-tai Chen

Automatic imaging of earthquake rupture processes by iterative deconvolution and stacking of high‐rate GPS and strong motion seismograms

By combining the complementary advantages of conventional network inversion and backprojection methods, we have developed an iterative deconvolution and stacking (IDS) approach for imaging earthquake rupture processes with near-field complete waveform data. This new approach does not need any manual adjustment of the physical (empirical) constraints, such as restricting the rupture time and duration, and smoothing the spatiotemporal slip distribution. Therefore, it has the ability to image complex multiple ruptures automatically. The advantages of the IDS method over traditional linear or nonlinear optimization algorithms are demonstrated by the case studies of the 2008 Wenchuan and 2011 Tohoku earthquakes. For such large earthquakes, the IDS method is considerably more stable and efficient than previous inversion methods. Additionally, the robustness of this method is demonstrated by comprehensive synthetic tests, indicating its potential contribution to tsunami and earthquake early warning and rapid response systems. It is also shown that the IDS method can be used for teleseismic waveform inversions. For the two major earthquakes discussed here, the IDS method can provide, without tuning any physical or empirical constraints, teleseismic rupture models consistent with those derived from the near-field GPS and strong motion data.

Stability of rapid finite‐fault inversion for the 2014 Mw6.1 South Napa earthquake

Local seismograms are useful for rapidly reconstructing kinematic finite-fault sources, but the results often depend not only on the data coverage but also on uncertainties of parameters (e.g., hypocentral location and fault geometry) used as a priori information during the inversion. An automatic scheme was applied to offline tests for the 2014 South Napa earthquake. In the case of retrospective full-waveform inversions, a network with station spacing of 10 km within the epicentral distance of 30 km is able to provide adequate stable key source parameters if the preestimated hypocenter and fault orientation are accurate of ±5 km and ±15°, respectively. In simulated real-time inversions, the magnitude reaches Mw6.0 at 13 s, and the slip distribution matches that from the retrospective inversion at about 22–28 s after the origin time of the earthquake. These results are meaningful for estimating the lead time of a catastrophic seismic event.

Comment on the paper “Normal and shear stress acting on arbitrarily oriented faults, earthquake energy, crustal GPE change, and the coefficient of friction” by P. P. Zhu

In his paper “Normal and shear stress acting on arbitrarily oriented faults, earthquake energy, crustal GPE change, and the coefficient of friction”, Zhu (2013) tried to theoretically solve the calculation of the fundamental parameters in seismology. These parameters include the normal and shear stresses acting on arbitrary oriented faults, the earthquake energy, crustal gravitational potential energy (GPE) change (hereon abbreviation or symbol in parenthesis is that used in Zhu’s paper), and the coefficient of friction. He especially emphasized the importance of gravitational potential energy (GPE) change, and stated that “many geophysicists accepted the idea of partitioning earthquake energy into radiated seismic energy (ER), friction energy (EF), and rupture energy (ERP) without consideration of crustal gravitational potential energy (GPE) change (e.g. Kanamori 2001; Abercrombie et al. 2006; Kanamori and Rivera 2006),” and that “the research on the earthquake energy budget stayed in qualitative analysis for a long time (e.g. Abercrombie et al. 2006).” In this short note, I will comment on the fundamental idea presented in Zhu’s paper (Zhu 2013) and will point out that his statement is incorrect. The energy balance in faulting was discussed very early and completely by Kostrov et al. (1969), Kostrov (1974, 1975), Dahlen (1977), Kostrov and Das (1988), and Dahlen and Tromp (1998), and a simplified and easily understood discussion of the energy changes involved in faulting within a self-gravitational body was given by Savage and Walsh (1978). The model earth Savage and Walsh (1978) used is a simple one. In their model, the fault is represented by a displacement dislocation buried in a self-gravitating earth subject to initial strain but free from external forces. They found for the total change in elastic strain energy (ESE) ΔEel is