Incomplete earthquake catalogs, especially for early aftershocks, pose challenges for accurate seismological analysis. This study introduces Auto-Biscale Empirical Transformation Application (AutoBETA), a fully automated earthquake data replenishment tool that builds upon previous semiautomated approaches by integrating gridbased density analysis with flexible missing region identification. This tool also supports user-defined polygons and hybrid strategies (union or intersection) to incorporate expert knowledge. We applied AutoBETA to one synthetic incomplete catalog and four real-earthquake catalogs: the 2008 Mw 7.9 Wenchuan, 2024 Mw 7.5 Noto, 2010 M 5.26 Baja California, and 2016 M 6.06 Norcia sequences. The analyses were conducted using magnitude thresholds of M >= 3.0, M >= 2.0, M >= 1.0, and M >= 2.0. After 100 fully automated iterations, the method replenished 43.9%, 40.0%, 40.5%, and 44.8% of the final catalogs. These results substantially improve catalog completeness, enabling more robust aftershock modeling and statistical analysis. AutoBETA is implemented in Python and is available as open-source software on GitHub.
The complex accretionary tectonics of Borneo record a history of multiterrane convergence and extension dating back to the Mesozoic. Seismic anisotropy can provide key insights into the regional tectonic evolution. Given the complicated tectonic history, applying a complex anisotropy model may help reconcile the different observations reported in previous studies. In this study, we use seismic data from five long-running stations with a recording period of about 20 yr to systematically investigate the layered anisotropic structure in the upper mantle, based on splitting analyses of teleseismic core-mantle-boundary refracted and local S waves. The joint analysis reveals two layers of anisotropy within the lithosphere and asthenosphere, showing different patterns. The lithospheric anisotropy is strongly correlated with major geological structures. In southern Borneo, the fast orientations are parallel to the strikes of the Kuching and Meratus Suture zones, which likely reflects the Late Cretaceous tectonic accretion along these boundaries. In northern Borneo, seismic anisotropy mainly records paleocollisional deformation related to the Sabah orogeny, which was induced by ProtoSouth China Sea subduction from the mid Eocene to early Miocene. The corresponding remnant slab is now located at depths that are too great to have a strong influence on the present-day mantle flow. This is supported by the asthenospheric anisotropy, which shows a dominant fast orientation of west-northwest-east-southeast that is consistent with the absolute plate motion of the Sunda plate. The anisotropy can be explained by the lattice-preferred orientation of olivine, which is related to a mantle flow field driven by the overriding plate motion and/or geodynamic processes within the asthenosphere associated with nearby subduction zones. Notably, the plastic flow is locally deflected by a lithospheric keel beneath eastern Borneo, which leads to the observed north- south-oriented anisotropy and a deflected flow pattern.
Understanding deformation patterns and rupture sources near the junction of the Ryukyu trench and the Longitudinal Valley in northeastern Taiwan is critical for seismic hazard assessment. We model the coseismic slip of the 2024 Mw 7.3 Hualien earthquake using onshore and seafloor geodetic data together with relocated seismicity. The rupture involves a deep 70 degrees east-dipping Longitudinal Valley fault and a 35 degrees west-dipping offshore fault, with maximum slips of 2.3 and 1.1 m, respectively. These faults released comparable amounts of geodetic moment, each equivalent to an Mw 7.1 event. The 2024 event and preceding offshore damaging earthquakes suggest that structures offshore Hualien accommodate a substantial portion of plate convergence. This interpretation is further supported by the sharp decrease in Global Navigation Satellite System secular velocities and shortening rates, as well as the seaward propagation of the Central Range fault from southern to northern Longitudinal Valley.
The 2024 Feidong earthquake swarm (maximum magnitude M 4.7) in the seismically quiet Hefei segment of the Tanlu fault zone (TLFZ) raises critical questions about its potential for larger earthquakes. We conducted 3D magnetotelluric imaging to obtain the crustal resistivity structure of the Hefei segment of the TLFZ. The results reveal a large-scale, Tanlu high-resistivity belt (TLRB) along the fault. Its southern segment (R1S) acts as a giant, rigid barrier that inhibits dextral strike-slip motion on the TLFZ. The Feidong earthquake swarm occurred in the structurally weak zone on the western flank of the central TLRB, near the western branch of the TLFZ. A local barrier effectively impeded northeastward rupture propagation. It shares geometric similarities with some seismogenic asperities observed in other strong earthquakes. However, the persistently low fault activity and seismic energy release indicate that current regional tectonic stresses are insufficient to overcome this local barrier, suggesting a low risk of strong earthquakes.
We use Coda envelope calibration to derive moment magnitude and apparent stress measurements for shallow earthquakes across Alaska. We base this on a set of similar to 70 reference moment magnitude (3.6 < M-w < 5.2) from the National Earthquake Information Center and 13 reference apparent stress (6a) estimates obtained from the coda spectral ratios method. We use the Coda Calibration Tool to correct for the low Q observed at surface stations, which allows us to produce nearly identical source spectra across the region, including spectra from colocated surface and borehole stations. After validating the calibration, we use it to calculate Mw for 700 shallow earthquakes and apparent stress for 200 events. This dataset allows us to develop a new conversion relationship between M-w and M-L using an orthogonal regression method that accounts for uncertainty in both M-L and M-w. This conversion is valid for shallow events in mainland Alaska. We observe a modest magnitude dependence in apparent stress, in agreement with previous studies. When considering spatial variation across the state, we accounted for this magnitude dependence by calculating psi(a)-a version of apparent stress (sigma(a)) with the magnitude effect removed. We further introduce phi(a)-a magnitude and depth-detrended version of 6a. This measure accounts for the magnitude and the slight depth dependence observed in the multiple linear regression model. The final detrended values reveal spatial variations in apparent stress across mainland Alaska, with relatively higher values in south-central Alaska, northern Alaska (Kaktovik region), and two events located on the Tintina fault.
