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Predicting the onset and timing of fault failure is one of the ultimate goals of seismology. However, our current understanding of the earthquake preparation and nucleation process is limited. One direction towards understanding this process is looking at precursory signals preceding large earthquakes. Previous laboratory experiments have studied robust precursory signals, observed as temporal changes in pressure and shear wave velocities during the seismic cycle. The effects of such precursory velocity changes on the seismic cycle are not well understood. We use numerical models to simulate fully-dynamic earthquake cycles in 2D strike-slip fault systems with antiplane geometry, surrounded by a narrow fault-parallel damage zone. By imposing shear wave velocity changes inside fault damage zones, we investigate the effects of these precursors on multiple stages of the seismic cycle, including nucleation, coseismic, postseismic, and interseismic stages. Our modeling results show a wide spectrum of fault-slip behaviors including fast earthquakes, slow-slip events, and variable creep. One primary effect of the imposed velocity precursor is the facilitation of the otherwise slow-slip event to grow into a fully dynamic earthquake. Furthermore, the onset time of these precursors have significant effects on the nucleation phase of the earthquakes, and earlier onset of precursors causes the earthquakes to nucleate earlier with a smaller nucleation size. Our results highlight the importance of short and long-term monitoring of fault zone structures for better assessment of regional seismic hazard.
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Foreshock properties illuminate nucleation processes of slow and fast laboratory earthquakes
Abstract Understanding the connection between seismic activity and the earthquake nucleation process is a fundamental goal in earthquake seismology with important implications for earthquake early warning systems and forecasting. We use high-resolution acoustic emission (AE) waveform measurements from laboratory stick-slip experiments that span a spectrum of slow to fast slip rates to probe spatiotemporal properties of laboratory foreshocks and nucleation processes. We measure waveform similarity and pairwise differential travel-times (DTT) between AEs throughout the seismic cycle. AEs broadcasted prior to slow labquakes have small DTT and high waveform similarity relative to fast labquakes. We show that during slow stick-slip, the fault never fully locks, and waveform similarity and pairwise differential travel times do not evolve throughout the seismic cycle. In contrast, fast laboratory earthquakes are preceded by a rapid increase in waveform similarity late in the seismic cycle and a reduction in differential travel times, indicating that AEs begin to coalesce as the fault slip velocity increases leading up to failure. These observations point to key differences in the nucleation process of slow and fast labquakes and suggest that the spatiotemporal evolution of laboratory foreshocks is linked to fault slip velocity.
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- Award ID(s):
- 2121666
- PAR ID:
- 10427188
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 14
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Allison Bent, Editor-in-Chief (Ed.)Seismic data are generally scrutinized for repeating earthquakes (REs) to evaluate slip rates, changes in the mechanical properties of a fault zone, and accelerating nucleation processes in foreshock and aftershock sequences. They are also used to study velocity changes in the medium, earthquake physics and prediction, and for constraining creep rate models at depth. For a robust detection of repeaters, multiple constraints and different parameter configurations related to waveform similarity have been proposed to measure cross‐correlation values at a local seismic network and evaluate the location of overlapping sources. In this work, we developed a Python code to identify REs (FINDRES), inspired by previous literature, which combines both seismic waveform similarity and differential S‐P travel time measured at each seismic station. A cross‐spectral method is applied to evaluate precise differential arrival travel times between earthquake pairs, allowing a subsample precision and increasing the capacity to resolve an overlapping common source radius. FINDRES is versatile and works with and without P‐ and S‐wave phase pickings, and has been validated using synthetic and real data, and provides reliable results. It would contribute to the implementation of open‐source Python packages in seismology, supporting the activities of researchers and the reproducibility of scientific results.more » « less
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null (Ed.)Earthquake prediction is the holy grail of seismology. Many previous studies have searched for robust precursory signals to inform us of imminent earthquakes, the most significant of which are seen in laboratory experiments as temporal changes in pressure and shear wave velocities during the seismic cycle. Similar changes are seen in natural faults and the surrounding structurally complex network of fractures with nested hierarchy of localized deformation, referred to as fault damage zone. However, little is known whether such temporal changes in material properties contains any precursory signals for imminent earthquakes.Conversely, the effect of precursory velocity changes on the seismic cycle is not well understood. By imposing shear wave velocity changes in fault damage zones, we investigate the effects of these precursors on multiple stages of the seismic cycle, including nucleation, coseismic, postseismic, and interseismic stages. We perform 2D fully dynamic earthquake cycle simulations with a fault-parallel damage zone for strike-slip fault systems with antiplane geometry. The fault is governed by rate-state-dependent friction laws, and the fault damage zone material is considered elastic. Our preliminary results show that the temporal onset of shear wave velocity drop causes a reduction in earthquake recurrence intervals over the seismic cycle. Furthermore, a dynamic earthquake rupture within the seismic cycle terminates much faster and abruptly in models with precursory velocity changes. We will also discuss how the precursory velocity changes affect the fault-slip behavior, including fast-slip, slow-slip, and aseismic creep, for different amplitudes of shear wave velocity changes at different compliance contrast of the fault damage zones. Our results highlight the importance of short and long-term monitoring of fault zone structures for better assessment of regional seismic hazard.more » « less
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