Many of these studies aim to automatically pick P and S arrivals, especially the signals of microseismicity buried under noises. Dozens of DL models prove to be efficient in detecting phases of local events (epicentral distance smaller than 300 km) (
An Mw 7.8 earthquake occurred on the East Anatolian Fault (EAF) and the secondary Narlı Fault (NF) on Feb 6, 2023, closely followed by an Mw 7.5 event on the Sürgü Fault 9 hours later. We analyze the distant and local seismic data, high-rate GPS recordings, and radar satellite images by Slowness Enhanced Back-Projection and joint Finite Fault Inversion for the Mw 7.8 event to resolve its rupture process. The rupture first initiates and propagates on the NF. After reaching the junction with the EAF, it propagates bilaterally on the EAF, extending 120 km to the northeast at 3.05 km/s and 200 km to the southwest at 3.11 km/s. The southwest speed is further verified by local seismic recordings and the absence of Mach surface wave characteristics. Compared with the EAF, the NF features denser seismic activity in recent decades, suggesting that it was more favorable for rupture nucleation. The EAF segments where the largest coseismic slip occurred have been relatively quiescent since the late 1800s. But the coseismic slip is much larger than the slip deficit accumulated during this period, which could be attributed to an ~900-year supercycle. The EAF geometry is similar to other active fault systems, such as the San Andreas Fault (SAF) and San Jacinto Fault (SJF). Considering high slip rates, resemblant supercycle mode, and the lack of large earthquakes on the southern SAF and SJF since 1857, an M8 earthquake could potentially occur there if most moment accumulation is released at once.
We explore the potential of the adjoint-state full waveform tsunami inversion method for tsunami warning and source imaging using S-net, an array of ocean bottom pressure gauges. Compared to finite-fault tsunami source inversions, the method we use does not require as densely gridded Green’s functions to obtain a high resolution result, thus reducing computation time. What is required is a dense instrument network with good azimuthal coverage. The S-net pressure gauges fulfill this requirement and reduce the data collection time, thus making it possible to invert the recordings for the tsunami source and issue a timely tsunami warning. We apply our method to synthetic waveforms of the 2011 Mw 9.0 Tohoku earthquake and tsunami as well as data from the 2016 Mw 6.9 Fukushima earthquake. The results of the synthetic tests show that using the first 5 minutes of the waveforms, the adjoint-state inversion method achieves good performance with an average accuracy score of 93%, with the error of predicted wave amplitudes ranging between -5.6 to 1.9 m. Our application to the 2016 Fukushima earthquake shows the required waveform duration to achieve accurate inversions for smaller events is longer than that of a larger event. However, using the first 25 minutes of the waveforms, the inversion yields a tsunami source that is sufficient for making accurate predictions of arrival times and amplitudes. Assuming a uniformly distributed fault slip, we estimated a stress drop for the latter event to be 4.6 MPa, which is in line with estimations from recent studies.
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