Microseismicity Simulated on Asperity‐Like Fault Patches: On Scaling of Seismic Moment With Duration and Seismological Estimates of Stress Drops

Lin, Yen-Yu; Lapusta, N.

doi:10.1029/2018gl078650

Cited by 28 publications

(35 citation statements)

References 71 publications

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“…Such high values were required in their study to fit the shape of the moment rate functions. Note that the stress drops inferences can be highly uncertain (e.g., Kaneko & Shearer, ; Lin & Lapusta, ), but our study will show that these estimates are consistent with a range of other observations about the SF and LA repeaters.…”

Section: Introduction: Repeating Sf and La Earthquake Sequencessupporting

confidence: 80%

Modeling High Stress Drops, Scaling, Interaction, and Irregularity of Repeating Earthquake Sequences Near Parkfield

Lui

Lapusta

2018

JGR Solid Earth

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Repeating earthquake sequences have been actively investigated to clarify many aspects of earthquake physics. The two particularly well‐studied sequences, known as the Los Angeles and San Francisco repeaters, have several intriguing observations, including their long (for the seismic moment) recurrence times that would suggest stress drops of 300 MPa based on typical assumptions, near‐syncronized timing prior to 2004, and higher than typical inferred stress drops (of 25 to 65 MPa, up to 90 MPa locally), but not as high as the recurrence times suggest. Here we show that all these observations are self‐consistent, in the sense that they can be reproduced in a single fault model. The suitable models build on the standard rate‐and‐state fault models, with velocity‐weakening patches imbedded into a velocity‐strengthening region, by adding either enhanced dynamic weakening during seismic slip or elevated normal stress on the patches, or both, to allow for the higher stress drops. Such models are able to match the observed average properties of the San Francisco and Los Angeles repeaters, as well as the overall nontrivial scaling between the recurrence time and seismic moment exhibited by many repeating sequences as a whole, for reasonable parameter choices based on experiments and theoretical studies. These models are characterized by the occurrence of substantial and variable aseismic slip at the locations of the repeating sources, which explains their atypical relation between recurrence interval and seismic moment, induces variability in the repeating source properties as observed, and results in their neither slip‐ nor time‐predictable behavior.

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Section: Introduction: Repeating Sf and La Earthquake Sequencessupporting

confidence: 80%

Modeling High Stress Drops, Scaling, Interaction, and Irregularity of Repeating Earthquake Sequences Near Parkfield

Lui

Lapusta

2018

JGR Solid Earth

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“…One physical explanation for the systematic tendencies for unilateral directivity in earthquakes is from rate‐ and state‐dependent friction. When the nucleation size

h

is much smaller than the potential seismogenic region, this results in ruptures that tend to propagate unilaterally (e.g., Lin & Lapusta, ; Michel et al, ). However, the expected rates of unilateral ruptures for this type of physical model have not been analyzed rigorously.…”

Section: Discussionmentioning

confidence: 99%

“…region, this results in ruptures that tend to propagate unilaterally (e.g., Lin & Lapusta, 2018;Michel et al, 2017). However, the expected rates of unilateral ruptures for this type of physical model have not been analyzed rigorously.…”

Section: The Importance Of Studying Directivity Modesmentioning

confidence: 99%

“…This model has led to a considerable body of numerical and observational studies (e.g., Ampuero & Ben-Zion, 2008;Brietzke et al, 2009;Zaliapin & Ben-Zion, 2011) and also generated discussion over its role in earthquake physics (Andrews & Harris, 2005;Ben-Zion, 2006a, 2006bHarris & Day, 2005). Other models may anticipate earthquakes to rupture with unilateral directivity as a frictional phenomenon, such as when the nucleation size is much smaller than the size of a seismogenic patch (e.g., Lin & Lapusta, 2018;Michel et al, 2017). It is desirable to better understand the relevance of these models to earthquakes in nature and whether there are resolvable differences in the properties of faults that can lead to different physics.…”

Section: Introductionmentioning

confidence: 99%

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Directivity Modes of Earthquake Populations with Unsupervised Learning

et al. 2020

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We present a novel approach for resolving modes of rupture directivity in large populations of earthquakes. A seismic spectral decomposition technique is used to first produce relative measurements of radiated energy for earthquakes in a spatially compact cluster. The azimuthal distribution of energy for each earthquake is then assumed to result from one of several distinct modes of rupture propagation. Rather than fitting a kinematic rupture model to determine the most likely mode of rupture propagation, we instead treat the modes as latent variables and learn them with a Gaussian mixture model. The mixture model simultaneously determines the number of events that best identify with each mode. The technique is demonstrated on four datasets in California, each with compact clusters of several thousand earthquakes with comparable slip mechanisms. We show that the datasets naturally decompose into distinct rupture propagation modes that correspond to different rupture directions, and the fault plane is unambiguously identified for all cases. We find that these small earthquakes exhibit unilateral ruptures 63–73% of the time on average. The results provide important observational constraints on the physics of earthquakes and faults.

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“…The generality of the inferred magnitude invariance of stress drops is still a topic of ongoing research, with some observations indicating that some individual earthquake sequences may exhibit mildly increasing trends in stress drop with increasing moment (e.g., Cocco et al, 2016;Viesca & Garagash, 2015). The interpretation and reliability of the stress drops estimates have been actively studied recently, with indications that the current standard methods of estimating stress drops can introduce some significant discrepancies between the actual and inferred stress drops (e.g., Kaneko & Shearer, 2014, 2015Lin & Lapusta, 2018;McGuire & Kaneko, 2018;Noda et al, 2013). However, there are no indications at present that the overall nearly magnitude-invariant trend should be questioned.…”

Section: Introductionmentioning

confidence: 99%

Nearly Magnitude‐Invariant Stress Drops in Simulated Crack‐Like Earthquake Sequences on Rate‐and‐State Faults with Thermal Pressurization of Pore Fluids

2020

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Stress drops, inferred to be magnitude‐invariant, are a key characteristic used to describe natural earthquakes. Theoretical studies and laboratory experiments indicate that enhanced dynamic weakening, such as thermal pressurization of pore fluids, may be present on natural faults. At first glance, magnitude invariance of stress drops and enhanced dynamic weakening seem incompatible since larger events may experience greater weakening and should thus have lower final stresses and higher stress drops. We hypothesize that enhanced dynamic weakening can be reconciled with magnitude‐invariant stress drops due to larger events having lower average prestress when compared to smaller events. We conduct numerical simulations of long‐term earthquake sequences in fault models with rate‐and‐state friction and thermal pressurization, and in the parameter regime that results mostly in crack‐like ruptures, we find that such models can explain both the observationally inferred stress drop invariance and increasing breakdown energy with event magnitude. Smaller events indeed have larger average initial stresses than medium‐sized events, and we find nearly constant stress drops for events spanning up to two orders of magnitude in average slip, comparable to approximately six orders of magnitude in seismic moment. Segment‐spanning events have more complex behavior, which depends on the properties of the arresting velocity‐strengthening region at the edges of the faults.

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Microseismicity Simulated on Asperity‐Like Fault Patches: On Scaling of Seismic Moment With Duration and Seismological Estimates of Stress Drops

Cited by 28 publications

References 71 publications

Modeling High Stress Drops, Scaling, Interaction, and Irregularity of Repeating Earthquake Sequences Near Parkfield

Modeling High Stress Drops, Scaling, Interaction, and Irregularity of Repeating Earthquake Sequences Near Parkfield

Directivity Modes of Earthquake Populations with Unsupervised Learning

Nearly Magnitude‐Invariant Stress Drops in Simulated Crack‐Like Earthquake Sequences on Rate‐and‐State Faults with Thermal Pressurization of Pore Fluids

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