Stress‐Drop Variability of Shallow Earthquakes Extracted from a Global Database of Source Time Functions

Courboulex, Françoise; Vallée, Martin; Causse, Mathieu; Chounet, Agnès

doi:10.1785/0220150283

Cited by 48 publications

(43 citation statements)

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“…This database has already been exploited to show that the stress drop increase with depth follows the medium rigidity increase, implying a constant strain drop Δ ε between 0‐ and 650‐km depth (Vallée, ). It has also been used to explore the global stress drop variability for shallow earthquakes, which is found to be reduced relative to other global databases (Courboulex et al, ). The epistemic variability is hence reduced, and the observed variability reflects more closely the actual diversity of rupture processes.…”

Section: Introductionmentioning

confidence: 99%

“…This vast class of earthquakes has some seismic characteristics which can be distinguished from the ones of earthquakes observed in other contexts. Analysis of their corner frequencies (Allmann & Shearer, ) or their STFs durations (Courboulex et al, ; Houston, ) show that they are in average less impulsive than intraplate earthquakes. Consistently, they are also characterized by a lower apparent stress (Choy & Boatwright, ).…”

Section: Introductionmentioning

confidence: 99%

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Global and Interregion Characterization of Subduction Interface Earthquakes Derived From Source Time Functions Properties

Chounet

Vallée

2018

JGR Solid Earth

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Source time functions (STFs) describe how the seismic moment rate is released with time, and carry information on integral rupture properties, such as static stress drop and radiated energy. In this study, we systematically analyze a set of 1,433 STFs extracted from the SCARDEC method (Vallée and Douet, 2016, https://doi.org/10.1016/j.pepi.2016.05.012), containing the Mw≥5.6, shallow (z≤70 km) earthquakes with dip‐slip mechanism that occurred between 1992 and 2014. At the global scale, STFs properties indicate scale invariance of stress drop and scaled radiated energy with magnitude. In a second step, these source parameters are investigated in light of the tectonic context of the earthquakes: in agreement with other approaches, we observe that subduction interface earthquakes have lower stress drop and scaled radiated energy relative to all other earthquakes (e.g., crustal earthquakes). Finally, a focus on subduction interface earthquakes (approximately 800 earthquakes) is done by considering 18 regional segments of subduction zones. We find that these segments do not have the same signature in terms of macroscopic rupture properties, which means that large‐scale plate convergence and mechanical properties influence rupture behavior. In a given segment, local heterogeneities of stress drop or radiated energy can be associated with local features of the subduction zone: in particular, we find that low coupled zones generate earthquakes with low stress drop and scaled radiated energy. This last feature, also observed at a larger scale, suggests a positive correlation between coupling and stress drop.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Global and Interregion Characterization of Subduction Interface Earthquakes Derived From Source Time Functions Properties

Chounet

Vallée

2018

JGR Solid Earth

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“…In (b) and (e) earthquakes have a typical source duration T t = ( M 0 /10 16 N.m) 1/3 (Houston, ), with M 0 the seismic moment, while in (a) and (d) their durations T − are shorter, and in (c) and (f) their durations T + are longer. The latter durations are chosen according to

T_{+ false/ -} = \exp false(\ln false(T_{t} false) \pm σ_{T} false)

, where σ T = 0.35 is the empirical standard error of the lognormal duration distribution observed by Courboulex et al (). PEGS are simulated using the normal‐mode approach using a point source at 20‐km depth with an isosceles triangular moment rate function.…”

Section: Discussionmentioning

confidence: 99%

Multiple Observations of the Prompt Elastogravity Signals Heralding Direct Seismic Waves

Vallée

Juhel

2019

JGR Solid Earth

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The recent first observations of the prompt elastogravity signals (PEGS) induced by the 2011 Mw = 9.1 Tohoku megathrust earthquake generated interest in how these signals might best be observed, especially for lower‐magnitude events. Simulations of these signals preceding the direct P wave, for different depths and focal mechanisms, first reveal that shallow strike‐slip earthquakes offer a better detection potential than subduction megathrust earthquakes. Consistently, clear PEGS are observed at several broadband seismometers during the 2012 Mw = 8.6 Wharton Basin earthquake. Due to their short source durations, large deep earthquakes are then shown to have an even larger detection potential, confirmed by the successful seismological observations for the 2018 Mw = 8.2 Fiji and 1994 Mw = 8.2 Bolivia earthquakes. Detection is even improved when an earthquake is recorded by a number of good‐quality stations, allowing for stacking techniques. Thanks to the deployment of the USArray network across Alaska, the recent 2018 Mw = 7.9 off‐Alaska earthquake (strike slip) is thus observed with an excellent signal‐to‐noise ratio. Array stacking is also shown to reveal the PEGS induced by the large 2010 Mw = 8.8 Maule megathrust earthquake, for which individual observations are impeded by the long‐lasting radiation generated by a distant large earthquake. As a whole, we show new observations and successful modeling of the PEGS for five earthquakes in the 7.9–8.8 magnitude range. These findings demonstrate that, even without considering promising future instruments, the PEGS detection is not restricted to exceptional events, confirming their potential for magnitude and focal mechanism determination within the few minutes following a large earthquake.

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“…To do so, we build a synthetic catalog of bimodal STFs, by summing two subevents growing both as

\overset{M}{true} false(t false) = α {false(t - t_{d} false)}^{n}

where α and n randomly vary around the observational values of α d and n d . t d =0 for the first subevent and t d take random values between 0 and T 0 /2 for the second subevent, where the STF total duration T 0 takes into account the observed variability around its magnitude‐dependent scaling law (Courboulex et al, ). By also varying the relative durations (and hence moments) between the first and the second subevent, we generate a synthetic catalog with a large diversity, mimicking the main STF characteristics observed in the SCARDEC catalog: simple STFs with early development phases are obtained when the first subevent dominates, while complex ruptures, with delayed development phases, are simulated when the second subevent dominates.…”

Section: Different Behaviors Between Development Phase and Early Ruptmentioning

confidence: 99%

How Does Seismic Rupture Accelerate? Observational Insights From Earthquake Source Time Functions

2019

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Observation of the seismic process for a large earthquake population is of key interest to detect potential magnitude‐dependent behaviors and, more generally, to quantify how seismic rupture develops. In contrast with studies focusing on the first radiated waves, we here propose to characterize the growing phase leading to the main seismic moment release episode(s), which we refer to as the development phase. Our analysis uses the 2,221 teleseismic source time functions (STFs) of shallow dip‐slip earthquakes provided by the global SCARDEC database and consists in measuring the moment acceleration during the development phase at prescribed moment rates. This approach is therefore insensitive to hypocentral time uncertainties and aims at quantifying how seismic ruptures accelerate, independently of when they accelerate. Our results first show that rupture acceleration does not exhibit any magnitude‐dependent signal emerging above the intrinsic measurements variability. We thus use the full STF catalog to characterize the moment rate trueṀd of the development phase and show that, on average, trueṀdfalse(tfalse)∝tnd with nd equal to 2.7. This time evolution therefore does not follow the steady t2 growth expected for classical circular crack models, which indicates that stress drop and/or rupture velocity transiently vary during the development phase. We finally illustrate with a synthetic STF catalog that, due to initial rupture variability, approaches based on hypocentral time are not expected to fully characterize the behavior of the development phase.

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Stress‐Drop Variability of Shallow Earthquakes Extracted from a Global Database of Source Time Functions

Abstract: International audienc

Cited by 48 publications

References 43 publications

Global and Interregion Characterization of Subduction Interface Earthquakes Derived From Source Time Functions Properties

Global and Interregion Characterization of Subduction Interface Earthquakes Derived From Source Time Functions Properties

Multiple Observations of the Prompt Elastogravity Signals Heralding Direct Seismic Waves

How Does Seismic Rupture Accelerate? Observational Insights From Earthquake Source Time Functions

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