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Abstract Extreme slip at shallow depths on subduction zone faults is a primary contributor to tsunami generation by earthquakes. Improving earthquake and tsunami risk assessment requires understanding the material and structural conditions that favor earthquake propagation to the trench. We use new biomarker thermal maturity indicators to identify seismic faults in drill core recovered from the Japan Trench subduction zone, which hosted 50 m of shallow slip during theMw9.1 2011 Tohoku-Oki earthquake. Our results show that multiple faults have hosted earthquakes with displacement ≥ 10 m, and each could have hosted many great earthquakes, illustrating an extensive history of great earthquake seismicity that caused large shallow slip. We find that lithologic contrasts in frictional properties do not necessarily determine the likelihood of large shallow slip or seismic hazard.
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Source Time Function Clustering Reveals Patterns in Earthquake Dynamics
Abstract We cluster a global database of 3529 Mw>5.5 earthquakes in 1995–2018 based on a dynamic time warping distance between earthquake source time functions (STFs). The clustering exhibits different degrees of complexity of the STF shapes and suggests an association between STF complexity and earthquake source parameters. Most of the thrust events have simple STF shapes across all depths. In contrast, earthquakes with complex STF shapes tend to be located at shallow depths in complicated tectonic regions, exhibit long source duration compared with others of similar magnitude, and tend to have strike-slip mechanisms. With 2D dynamic modeling of dynamic ruptures on heterogeneous fault properties, we find a systematic variation of the simulated STF complexity with frictional properties. Comparison between the observed and synthetic clustering distributions provides useful constraints on frictional properties. In particular, the characteristic slip-weakening distance could be constrained to be short (<0.1 m) and depth dependent if stress drop is in general constant.
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- Award ID(s):
- 1749556
- PAR ID:
- 10229803
- Date Published:
- Journal Name:
- Seismological Research Letters
- ISSN:
- 0895-0695
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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ABSTRACT Earthquake stress drop—a key parameter for describing the energetics of earthquake rupture—can be estimated in several different, but theoretically equivalent, ways. However, independent estimates for the same earthquakes sometimes differ significantly. We find that earthquake source complexity plays a significant role in why theoretically (for simple rupture models) equivalent methods produce different estimates. We apply time- and frequency-domain methods to estimate stress drops for real earthquakes in the SCARDEC (Seismic source ChAracteristics Retrieved from DEConvolving teleseismic body waves, Vallée and Douet, 2016) source time function (STF) database and analyze how rupture complexity drives stress-drop estimate discrepancies. Specifically, we identify two complexity metrics—Brune relative energy (BRE) and spectral decay—that parameterize an earthquake’s complexity relative to the standard Brune model and strongly correlate with the estimate discrepancies. We find that the observed systematic magnitude–stress-drop trends may reflect underlying changes in STF complexity, not necessarily trends in actual stress drop. Both the decay and BRE parameters vary systematically with magnitude, but whether this magnitude–complexity relationship is real remains unresolved.more » « less
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Faults are usually surrounded by damage zones associated with localized deformation. Here we use fully dynamic earthquake cycle simulations to quantify the behaviors of earthquakes in fault damage zones. We show that fault damage zones can make a significant contribution to the spatial and temporal seismicity distribution. Fault stress heterogeneities generated by fault zone waves persist over multiple earthquake cycles that, in turn, produce small earthquakes that are absent in homogeneous simulations with the same friction conditions. Shallow fault zones can produce a bimodal depth distribution of earthquakes with clustering of seismicity at both shallower and deeper depths. Fault zone healing during the interseismic period also promotes the penetration of aseismic slip into the locked region and reduces the sizes of fault asperities that host earthquakes. Hence, small and moderate subsurface earthquakes with irregular recurrence intervals are commonly observed in immature fault zone simulations with interseismic healing. To link our simulation results to geological observations, we will use simulated fault slip at different depths to infer the timing and recurrence intervals of earthquakes and discuss how such measurements can affect our understanding of earthquake behaviors. We will also show that the maturity and material properties of fault damage zones have strong influence on whether long-term earthquake characteristics are represented by single events.more » « less
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The development of multiple paleotemperature proxies over the last twenty years has led to an increasing number of coseismic temperature measurements collected across a variety of faults. Here we present the first compilation of coseismic temperature rise measurements and frictional energy estimates to investigate the contribution of frictional heating to the earthquake energy budget and how this varies over different fault and earthquake properties. This compilation demonstrates that there is no clear relationship between coseismic temperature and displacement or thickness of the principal slip zone. Coseismic temperature rise increases with the depth of faulting until ~5 km and below this depth temperature rise remains relatively constant. Frictional energy, similarly, increases with depth until ~5km. However, frictional energy is remarkably similar across all of the faults studied here, with most falling below 45 MJ/m2. Our results suggest that dynamic weakening mechanisms may limit frictional energy during coseismic slip. We also demonstrate a basic difference between small and large earthquakes by comparing frictional energy to other components of the earthquake energy budget. The energy budget for small earthquakes (<1-10 m of displacement) is dominated by frictional energy, while in large events (>1-10 m of displacement), frictional, radiated, and fracture energy contribute somewhat equally to the earthquake energy budget.more » « less
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Abstract On 19 September 2022, a major earthquake struck the northwestern Michoacán segment along the Mexican subduction zone. A slip model is obtained that satisfactorily explains geodetic, teleseismic, and tsunami observations of the 2022 event. The preferred model has a compact large-slip patch that extends up-dip and northwestward from the hypocenter and directly overlaps a 1973 Mw 7.6 rupture. Slip is concentrated offshore and below the coast at depths from 10 to 30 km with a peak value of ∼2.9 m, and there is no detected coseismic slip near the trench. The total seismic moment is 3.1×1020 N·m (Mw 7.6), 72% of which is concentrated in the first 30 s. Most aftershocks are distributed in an up-dip area of the mainshock that has small coseismic slip, suggesting near-complete strain release in the large-slip patch. Teleseismic P waveforms of the 2022 and 1973 earthquakes are similar in duration and complexity with high cross-correlation coefficients of 0.68–0.98 for long P to PP signal time windows, indicating that the 2022 earthquake is a quasi-repeat of the 1973 earthquake, possibly indicating persistent frictional properties. Both the events produced more complex P waveforms than comparable size events along Guerrero and Oaxaca, reflecting differences in patchy locking of the Mexican megathrust.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1785/0220200403
