Seismica

Seismo-Acoustic Meteoroid Observation Recording Database (SMORD): A Global Dataset and Deep-Learning Phase Picker for Meteoroid-Generated Air-to-Ground Coupled Seismic Waves

2026-07-03T14:07:45-04:00

Meteoroids impacting Earth's atmosphere generate acoustic waves that can couple into the ground and can be recorded by dense, globally distributed seismic networks. Thus, these records complement optical and radar observations, especially since seismic stations also operate in cloudy weather conditions and during daytime. However, open datasets that link meteoroid events to labeled seismic waveforms are scarce, limiting the development of automated detectors for meteoroid-induced seismo-acoustic signals. We introduce the Seismo-acoustic Meteoroid Observation Recording Database (SMORD), compiled by cross-referencing public meteoroid catalogs (International Meteor Organization fireball reports; NASA CNEOS fireball catalog) with seismic archives. Continuous waveforms are manually labeled for the first clear meteoroid-related onset of air-to-ground coupled seismic waves using a three-level pick-quality scheme. SMORD v1.0 contains 310 meteoroid events and 3,295 labeled arrivals across a global station set. Using SMORD labels, we train a PhaseNet picker in SeisBench with station-level splits and augmentation. On test data, the model achieves 91% precision and 94% recall at a 0.5 decision threshold (area-under-curve value 0.89), with median absolute timing error of 0.02~s (90% within c. ±0.3 s). We demonstrate automated onset detection and trajectory reconstruction for an April 2025 Adriatic fireball, highlighting the values of SMORD for rapid post-event analysis.

Paleoseismic history of the causative faults of the 2019 Ridgecrest, California earthquake sequence

2026-01-16T08:11:44-05:00

The July 2019 Ridgecrest sequence ruptured two nearly orthogonal faults, the left-lateral, NE-striking Salt Wells Valley fault (M_w6.4) and the right-lateral, NW-striking Paxton Ranch fault (M_w7.1), highlighting the hazard of multi-fault earthquakes in the Walker Lane. To test whether similar conjugate ruptures occurred previously, we excavated five paleoseismic trenches and constrained paleo-earthquake timing using luminescence ages. Salt Wells Valley exposures record the 2019 rupture and only one earlier surface-faulting earthquake (17-27 ka), indicating infrequent activity. In contrast, Paxton Ranch strata preserve two Holocene events (4.4-8.7 ka and 10.6-14.6 ka) and up to three late Pleistocene events (17 ka and older) in addition to 2019. These records indicate that rupture along the Paxton Ranch fault commonly occurs independently of the Salt Wells Valley fault. Slip rates based on 2019 displacements and these event intervals are 0.2-1.3 mm yr⁻¹ for Paxton Ranch and 0.01-0.09 mm yr⁻¹ for Salt Wells Valley. The 2019 sequence therefore represents an unusual pairing of an often-active dextral fault with a much less active sinistral fault. The contrasting recurrence and lack of overlap, together with regional paleoseismic patterns, indicate that synchronous rupture is not systematic but instead varies among faults within an evolving network. This suggests that seismic hazard reflects a fault system in which rupture is governed by time-dependent fault network interactions rather than independent, repeatable behavior of individual faults.

Crustal Thickness Variations Beneath the Western Indian Ocean Using Teleseismic P-Wave Coda Autocorrelations on Ocean-Bottom Seismic Data

2026-07-03T14:07:53-04:00

The western Indian Ocean is a key region for investigating lithospheric evolution, as it records a complex interplay of tectonic, magmatic, and mantle processes. Constraining crustal thickness across this area is therefore essential for understanding how these processes interact and shape the region's geodynamic development. In this study, we apply teleseismic P-wave coda autocorrelation to map crustal thickness across the western Indian Ocean using data from 54 ocean-bottom seismometers (OBSs) and 7 land-based seismic stations. Our results reveal pronounced lateral variations in crustal thickness, ranging from ~4.3 km beneath young oceanic crust near the Central Indian Ridge (CIR) to ~25.85 km along the eastern margin of Madagascar. The oceanic domain exhibits a mean crustal thickness of ~7.01 ± 0.27 km, consistent with global oceanic averages. Volcanic islands within the Mozambique Channel show crustal thicknesses between ~11.21 and 23.98 km, whereas those in the Mascarene Basin display values of ~10.73 km and ~14.63 km. These localized zones of crustal thickening beneath volcanic islands likely reflect long-lived magmatic underplating and hotspot-related intrusions. Collectively, these findings provide new quantitative constraints on the tectono-magmatic processes that govern crustal formation, modification, and isostatic compensation in this geodynamically complex region.

Integrated seismic monitoring reveals subsurface evolution during volcanic inflation at Askja volcano, Iceland

2026-07-13T07:07:18-04:00

Identifying volcanic transitions from quiescence to unrest and tracking subsurface evolution remains critically challenging. We analyzed continuous seismic records from Askja volcano (Iceland) from 2008--2024 using coda wave interferometry to track relative seismic velocity variations (dv/v) as a proxy for subsurface changes during renewed volcanic intrusion. This analysis is complemented with three additional methods: network covariance matrix analysis, Displacement Seismic Amplitude Ratio (DSAR) single-station analysis, and sensitivity kernel analysis, alongside GNSS, earthquake catalog, and meteorological datasets. Since August 2021, dv/v measurements revealed an abrupt transition from regular seasonal oscillations (±0.2\%) to predominantly negative values reaching -0.7\% near the inflation center, coinciding with 76 cm GNSS-detected ground uplift by August 2024. DSAR indicated higher seismic attenuation near the inflation source, suggesting volatile accumulation in the shallow subsurface through June 2022, followed by marked decreases associated with depressurization. Sensitivity kernel analysis demonstrated wave sensitivity reaches down to 3 km depth, encompassing the shallow reservoir levels. Integrated seismic observations revealed magma-induced seismic velocity drops, followed by system reorganization with frequency-dependent recovery, and finally establishment of a new state with hydrothermal circulation maintaining altered seismic properties. This approach demonstrates the effectiveness of continuous seismic monitoring for detecting volcanic unrest transitions and tracking evolving subsurface processes.