Tai-Lin Tseng

Depth‐dependent attenuation in the uppermost inner core from the Taiwan short period seismic array PKP data

Inner core attenuation properties from two spots were examined in detail using PKIKP and PKP(BC) phases with a distance range of between 147° and 154° as recorded by both the short-period regional seismic array in Taiwan and the broadband stations of the German Regional Seismic Network. The ray paths from the six South American events to Taiwan sampled the inner core region beneath the eastern part of the northern Pacific Ocean, while those from Fiji to Europe reflected the inner core boundary under the western part of the northern Pacific Ocean. Results of this study show the depth-dependent attenuation of Qp beneath the eastern part of the northern Pacific Ocean from 241±21.8 (at depths 270 km) with a weighted mean of 305±25.4 within the frequency band 0.5∼2.0Hz. The average Qp under the western part of the northern Pacific Ocean is 160±33.5 (0.5 ∼ 1.5Hz) which is consistent with that previously reported. It is found that Qp under the western part of the northern Pacific is clearly lower than that under the eastern part. This discrepancy might be related to regional variations in the uppermost inner core.

A 3-D spectral-element and frequency-wave number hybrid method for high-resolution seismic array imaging

We present a three-dimensional (3-D) hybrid method that interfaces the spectral-element method (SEM) with the frequency-wave number (FK) technique to model the propagation of teleseismic plane waves beneath seismic arrays. The accuracy of the resulting 3-D SEM-FK hybrid method is benchmarked against semianalytical FK solutions for 1-D models. The accuracy of 2.5-D modeling based on 2-D SEM-FK hybrid method is also investigated through comparisons to this 3-D hybrid method. Synthetic examples for structural models of the Alaska subduction zone and the central Tibet crust show that this method is capable of accurately capturing interactions between incident plane waves and local heterogeneities. This hybrid method presents an essential tool for the receiver function and scattering imaging community to verify and further improve their techniques. These numerical examples also show the promising future of the 3-D SEM-FK hybrid method in high-resolution regional seismic imaging based on waveform inversions of converted/scattered waves recorded by seismic array.

Erratum to Velocity Structure of the Tibetan Lithosphere: Constraints from P‐Wave Travel Times of Regional Earthquakes

Using data from regional earthquakes recorded by the Hi-CLIMB array in Tibet, we model P-wave arrival times to constrain the velocity structure in the crust and the upper mantle in central and western Tibet. Of more than 30 high-quality, regional seismic profiles that have been assembled, we have selected 10 that show excellent crustal and Pn arrivals for further analysis. Travel times from four events along the Hi-CLIMB array provide details on crustal velocities, and six events at regional distances to the array provide further constraints on Moho structure and upper-mantle-lid velocities. We use three-dimensional ray tracing to model the travel times, and the results indicate that the Moho beneath the Lhasa terrane of southern Tibet is over 73 km deep, with a Pn speed of about 8:2 km=s. The Qiangtang terrane north of the Bangong-Nujiang suture (BNS) shows a thinner crust, by up to 10 km, and a lower Pn speed of 7:8-7:9 km=s. Travel times from events to thewest and east of the array indicate that both Moho structure and mantle-lid velocities in the region are three-dimensional in nature but approximately follow the trend of the BNS. Although only a limited number of events were used for the travel-time modeling, the results are consistent with earlier results from teleseismic imaging using the Hi-CLIMB array.

A New Automatic Full‐Waveform Regional Moment Tensor Inversion Algorithm and Its Applications in the Taiwan AreaA New Automatic Full‐Waveform Regional MT Inversion Algorithm and Its Applications in the Taiwan Area

A new algorithm has been developed in this study that can automatically determine regional moment tensor (MT) and its centroid depth with real-time waveforms; it can do this within 2–4 min of an earthquake notice issued by the Central Weather Bureau (CWB). The program selects 3–7 BATS (Broadband Array in Taiwan for Seismology) stations based on three different strategies: best azimuthal distribution, highest signal-to-noise ratio, and shortest distances. The program then inverts MT solutions in parallel with various settings that include Moho depth of velocity models, frequency bands, and isotropic constraints. The optimal solution is determined via a search for the best waveform fit with an acceptable non-double-couple component that comes from the results of combinations of these inversion settings. Our new rapid MT report system greatly reduces the need for computational resources and avoids human judgments. By applying this full-scanning approach on BATS (named AutoBATS), we redetermine theMTs for over 3000 regional earthquakes that took place between 1996 and 2016, the goal being to provide the most up-to-date possible MT catalog for the Taiwan area. Overall, the AutoBATS MTs are consistent with the Global Centroid Moment Tensors, with a mean difference in the Kagan angle of 22:0° 16:6° andMw of −0:08 0:10. Those focal mechanisms better illuminate the tectonic structures, which is a result of the significantly improved resolving ability for shallow (< 10 km) and deep (> 140 km) earthquakes. With the new regional MT catalog, we refine the relationship between moment and local magnitudes: Mw 0:87ML 0:23 for the Taiwan region.