Exploring frictional velocity dependence as a mechanism for slow earthquake rupture

Mapping Intimacies ◽

10.5194/egusphere-egu2020-16538 ◽

2020 ◽

Author(s):

Julia Krogh ◽

Chris Marone

Keyword(s):

Slip Velocity ◽

Fault Slip ◽

Slow Slip ◽

Velocity Dependence ◽

Friction Modeling ◽

Slow Slip Events ◽

Slow Earthquake ◽

Stable Conditions ◽

Slow Earthquakes ◽

The Stability

Earthquakes fail through a spectrum of slip modes ranging from slow slip to fast elastodynamic rupture. Slow earthquakes, or slow-slip events, represent fault slip behaviors that involve quasi-dynamic, self-sustained rupture propagation. To better understand the mechanisms that limit the slip speed and propagation rates of slow slip, we focus on a particular parameter: the critical frictional weakening rate of the fault surface, kc. When kc is approximately equal to k, the elastic loading stiffness of the fault, complex fault slip behaviors including slow-slip events are observed. If kc has a negative dependence on slip velocity, acceleration during the coseismic phase could decrease kc until it approximates k, terminating in a slow earthquake. Here, we describe the results of laboratory experiments designed to quantify the dependence of kc on frictional slip velocity. We conducted double-direct shear experiments in a biaxial shearing apparatus with 3 mm-thick fault zones composed of quartz powder to simulate fault gouge. We focus on step decreases in slip velocity from 300 to 3 m/s that were performed for a range of normal stresses, from 10 to 20 MPa, which we know to be near the stability transition from stable to unstable sliding defined by k/kc ~ 1.0. Under stable conditions, rate-state friction modeling was used to determine kc for each velocity step. Our data provide direct insight on the stability transition associated with kc(V), including experiments for which slow-slip instabilities grew larger and faster throughout velocity-step sequences. Ultimately, both numerical modeling and observational data indicate that the velocity dependence of kc is an important parameter when considering the mechanisms of slow earthquake nucleation.&#160;

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Fault healing plays a key role in creating the spectrum of tectonic faulting styles from seismic to aseismic slip

10.5194/egusphere-egu2020-2761 ◽

2020 ◽

Author(s):

Chris Marone

Keyword(s):

Potential Energy ◽

Stress Drop ◽

Elastic Strain ◽

Stability Boundary ◽

Fault Slip ◽

Slow Slip ◽

Stick Slip ◽

Slow Earthquakes ◽

The Stability ◽

Fault Healing

Tectonic faults fail in a broad spectrum of modes ranging from aseismic creep to fast, ordinary, earthquakes modulated by elastodynamic rupture processes. Laboratory friction experiments with repetitive stick-slip failure have reproduced this complete range of modes with failure durations spanning several orders of magnitude. These works show that the frictional weakening rate with slip (i.e., the rheological critical stiffness kc =&#963;n(b-a)/Dc, where &#963;n&#160;is effective fault normal stress, Dc is the friction critical slip distance and (b-a) represents the friction rate parameter) is the primary control on the mode of slip, but higher-order effects are also important including variation of kc &#160;with slip velocity.&#160; Far from the stability boundary, stick-slip occurs when the rate of elastic unloading with slip k is small compared to the frictional weakening rate (i.e., k<<kc). Potential energy, in the form of stored elastic strain, drives rapid fault acceleration. Near the stability boundary, when k ~ kc, lab experiments document slow and quasi-dynamic failure events, consistent with the observation that earthquake stress drop is negligible for slow earthquakes. Lab data show that stick-slip stress drop decreases systematically as k/kc approaches 1 from below. There are two possible scenarios for slow slip near the stability boundary, although they are degenerate in most cases. 1) Fault slip relieves elastic stresses prior to failure and thus the potential energy needed to drive fast rupture is absent. 2) Elastic strain accumulates but the fault rheology is velocity strengthening or otherwise inconsistent with rapid slip, for example because the frictional weakening rate kc&#160; is low. &#160;In Scenario 1, slip can occur early in the seismic cycle, as creep, or later in the cycle when shear stress reaches a critical value for precursory slip. &#160;In either case, slip occurs because the rate of fault healing is low compared to the stressing rate. A low rate of fault healing can also explain Scenario 2 because the friction state evolution parameter b scales directly with the rate of fault healing and kc. Given that the friction parameter a is positive definite, the frictional healing rate (b) sets the scale of kc for a given value of Dc. Thus, while these two scenarios for slow slip appear distinct they both derive from the rate of fault healing.&#160; Exceptions would involve faults that are strongly velocity weakening (b-a) >>0 yet have negligible healing rates (b ~ 0), which is indeed rare.&#160; The rate of fault healing is expected to vary with mineralogy, effective stress, temperature and other factors. Thus, while we expect a systematic variation of seismic style with depth, associated with changes in kc, we should not be surprised to find a spectrum of faulting styles throughout the lithosphere, including a range of styles at a given location.&#160; Discoveries of seismic tremor, low frequency earthquakes, and other modes of fault slip are challenging our views of tectonic faulting and they highlight the need for close connections between field observations, detailed laboratory work and theoretical studies of friction and faulting.

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Observing seismic signatures of slow slip events with unsupervised learning

10.5194/egusphere-egu21-5603 ◽

2021 ◽

Author(s):

Leonard Seydoux ◽

Michel Campillo ◽

René Steinmann ◽

Randall Balestriero ◽

Maarten de Hoop

Keyword(s):

Clustering Algorithm ◽

Low Frequency ◽

Seismic Signal ◽

Geodetic Data ◽

Slow Slip ◽

Slow Slip Events ◽

Slow Slip Event ◽

Intermittent Behavior ◽

Slow Earthquakes ◽

Slip Event

Slow slip events are observed in geodetic data, and are occasionally associated with seismic signatures such as slow earthquakes (low-frequency earthquakes, tectonic tremors). In particular, it was shown that swarms of slow earthquake can correlate with slow slip events occurrence, and allowed to reveal the intermittent behavior of several slow slip events. This observation was possible thanks to detailed analysis of slow earthquakes catalogs and continuous geodetic data, but in every case, was limited to particular classes of seismic signatures. In the present study, we propose to infer the classes of seismic signals that best correlate with the observed geodetic data, including the slow slip event. We use a scattering network (a neural network with wavelet filters) in order to find meaningful signal features, and apply a hierarchical clustering algorithm in order to infer classes of seismic signal. We then apply a regression algorithm in order to predict the geodetic data, including slow slip events, from the occurrence of inferred seismic classes. This allow to (1) identify seismic signatures associated with the slow slip events as well as (2) infer the the contribution of each classes to the overall displacement observed in the geodetic data. We illustrate our strategy by revisiting the slow-slip event of 2006 that occurred beneath Guerrero, Mexico.

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An intraplate slow earthquake observed by a dense GPS network in Hokkaido, northernmost Japan

Geophysical Journal International ◽

10.1093/gji/ggu380 ◽

2014 ◽

Vol 200 (1) ◽

pp. 144-148 ◽

Cited By ~ 1

Author(s):

Mako Ohzono ◽

Hiroaki Takahashi ◽

Masayoshi Ichiyanagi

Keyword(s):

Subduction Zones ◽

Earthquake Swarm ◽

Tectonic Activity ◽

Maximum Magnitude ◽

Slow Slip ◽

Localized Deformation ◽

Slow Earthquake ◽

Magnitude Scaling ◽

Duration Magnitude ◽

Slow Earthquakes

Abstract An intraplate slow earthquake was detected in northernmost Hokkaido, Japan, by a dense network of the global navigation satellite system. Transient abnormal acceleration of <12 mm was observed during the period 2012 July to 2013 January (∼5.5 months) at several sites. The spatial displacement distribution suggests that a localized tectonic event caused localized deformation. Estimated fault parameter indicates very shallow-dip reverse faulting in the uppermost crust, with a total seismic moment of 1.75E + 17 N m (Mw 5.4). This fault geometry is probably consistent with detachment structure indicated by geological studies. A simultaneous earthquake swarm with the maximum magnitude M4.1 suggests a possibility that the slow slip triggered the seismic activity for unknown reasons. This slow earthquake is slower than its moment would indicate, with a duration–magnitude scaling relationship unlike either regular earthquakes or subduction slow slip events. This result indicates that even if the area is under different physical property from subduction zones, slow earthquake can occur by some causes. Slow earthquakes exist in remote regions away from subduction zones and might play an important role in strain release and tectonic activity.

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Stress triggering and the mechanics of fault slip behavior

10.5194/egusphere-egu2020-21610 ◽

2020 ◽

Author(s):

Marco Maria Scuderi ◽

Cristiano Collettini

Keyword(s):

Stress Field ◽

Normal Stress ◽

Stability Boundary ◽

Fault Slip ◽

Fault Gouge ◽

Recurrence Time ◽

Slow Slip ◽

Stick Slip ◽

Slow Slip Events ◽

Stress Changes

Dynamic changes in the stress field during the seismic cycle of tectonic faults can control frictional stability and the mode of fault slip. Small perturbation in the stress field, like those produced by tidal stresses can influence the evolution of frictional strength and fault stability with the potential of triggering a variety of slip behaviors. However, an open question that remains still poorly understood is how amplitude and frequency of stress changes influence the triggering of an instability and the associated slip behavior, i.e. slow or fast slip.Here we reproduce in the laboratory the spectrum of fault slip behaviors, from slow-slip to dynamic stick-slip, by matching the critical fault rheologic stiffness (kc) with the surrounding stiffness (k). We investigate the influence of normal stress variations on the slip style of a quartz rich fault gouge at the stability boundary, i.e. k/kc slightly less than one, by adopting two techniques: 1) instantaneous step-like changes and 2) sinusoidal variations in normal stress. For the latter case, modulations of normal stress were chosen to have amplitudes greater, less or equal to the typical stress drop observed during unperturbed experiments. Also, the period was varied to be greater, less or equal to the typical recurrence time of laboratory slow-slip events. During the experiments, we continuously record ultrasonic wave velocity to monitor the microphysical state of the fault. We find that frictional stability is profoundly affected by variation in normal stress giving rise to a variety of slip behaviors. Furthermore, during strain accumulation and fabric development, changes in normal stress permanently influence the microphysical state of the fault gouge increasing kc and producing a switch from slow to fast stick-slip. Our results indicate that perturbations in the stress state can trigger a variety of slip behaviors along the same fault patch. These results have important implications for the formulation of constitutive laws in the framework of rate- and state- friction, highlighting the necessity to account for the microphysical state of the fault in order to improve our understanding of frictional stability.

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Shallow slow slip events along the Nankai Trough detected by GNSS-A

Science Advances ◽

10.1126/sciadv.aay5786 ◽

2020 ◽

Vol 6 (3) ◽

pp. eaay5786 ◽

Cited By ~ 12

Author(s):

Yusuke Yokota ◽

Tadashi Ishikawa

Keyword(s):

Subduction Zones ◽

Nankai Trough ◽

Plate Boundary ◽

Low Frequency ◽

Satellite System ◽

Boundary Region ◽

Slow Slip ◽

Slow Slip Events ◽

Combination Technique ◽

Slow Earthquakes

Various slow earthquakes (SEQs), including tremors, very low frequency events, and slow slip events (SSEs), occur along megathrust zones. In a shallow plate boundary region, although many SEQs have been observed along pan-Pacific subduction zones, SSEs with a duration on the order of a year or with a large slip have not yet been detected due to difficulty in offshore observation. We try to statistically detect transient seafloor crustal deformations from seafloor geodetic data obtained by the Global Navigation Satellite System-Acoustic (GNSS-A) combination technique, which enables monitoring the seafloor absolute position. Here, we report the first detection of signals probably caused by shallow large SSEs along the Nankai Trough and indicate the timings and approximate locations of probable SSEs. The results show the existence of large SSEs around the shallow side of strong coupling regions and indicate the spatiotemporal relationship with other SEQ activities expected in past studies.

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Shallow slow earthquakes to decipher future catastrophic earthquakes in the Guerrero seismic gap.

10.21203/rs.3.rs-102838/v1 ◽

2020 ◽

Author(s):

Raymundo Plata-Martínez ◽

Satoshi Ide ◽

Masanao Shinohara ◽

Emmanuel Soliman Garcia Mortel ◽

Naoto Mizuno ◽

...

Keyword(s):

Seismogenic Zone ◽

Seismic Gap ◽

Slow Slip ◽

Dynamic Rupture ◽

Plate Interface ◽

Slow Slip Events ◽

Repeating Earthquakes ◽

Slow Earthquakes ◽

Slip Area ◽

Large Earthquakes

Abstract The Guerrero seismic gap is presumed to be a major source of seismic and tsunami hazard along the Mexican subduction zone. Until recently, there were limited observations to describe the shallow portion of the plate interface in Guerrero. For this reason, we deployed offshore instrumentation to gain new seismic data and identify the extent of the seismogenic zone inside the Guerrero gap. We discovered episodic shallow tremors and potential slow slip events which, together with repeating earthquakes, seismicity, residual gravity and residual bathymetry suggest that a portion of the shallow plate interface in the Guerrero seismic gap undergoes stable slip. This mechanical condition may not only explain the long return period of large earthquakes with origins inside the Guerrero seismic gap, but also reveal why the rupture from past M<8 earthquakes on adjacent megathrust fault segments did not propagate into the gap to encompass a larger slip area. Nevertheless, a large enough earthquake initiating nearby could rupture through the entire Guerrero seismic gap if driven by dynamic rupture effects.

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Unraveling the Origin of Slow Earthquakes

Eos ◽

10.1029/2019eo114011 ◽

2019 ◽

Vol 100 ◽

Author(s):

Terri Cook

Keyword(s):

Physical Properties ◽

Subduction Zone ◽

Slow Slip ◽

Tectonic Plate ◽

Plate Interface ◽

Change Over Time ◽

Slow Slip Events ◽

Slow Earthquakes ◽

Over Time

Different nucleation styles detected in five slow-slip events in the same area of Japan’s Ryukyu subduction zone suggest the physical properties along this tectonic plate interface change over time.

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Shallow slow earthquakes to decipher future catastrophic earthquakes in the Guerrero seismic gap

Nature Communications ◽

10.1038/s41467-021-24210-9 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

R. Plata-Martinez ◽

S. Ide ◽

M. Shinohara ◽

E. S. Garcia ◽

N. Mizuno ◽

...

Keyword(s):

Seismogenic Zone ◽

Seismic Gap ◽

Slow Slip ◽

Dynamic Rupture ◽

Plate Interface ◽

Slow Slip Events ◽

Repeating Earthquakes ◽

Residual Gravity ◽

Slow Earthquakes ◽

Large Earthquakes

AbstractThe Guerrero seismic gap is presumed to be a major source of seismic and tsunami hazard along the Mexican subduction zone. Until recently, there were limited observations at the shallow portion of the plate interface offshore Guerrero, so we deployed instruments there to better characterize the extent of the seismogenic zone. Here we report the discovery of episodic shallow tremors and potential slow slip events in Guerrero offshore. Their distribution, together with that of repeating earthquakes, seismicity, residual gravity and bathymetry, suggest that a portion of the shallow plate interface in the gap undergoes stable slip. This mechanical condition may not only explain the long return period of large earthquakes inside the gap, but also reveals why the rupture from past M < 8 earthquakes on adjacent megathrust segments did not propagate into the gap to result in much larger events. However, dynamic rupture effects could drive one of these nearby earthquakes to break through the entire Guerrero seismic gap.

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Effect of Ocean Fluid Changes on Pressure on the Seafloor: Ocean Assimilation Data Analysis on Warm-Core Rings off the Southeastern Coast of Hokkaido, Japan on an Interannual Timescale

Frontiers in Earth Science ◽

10.3389/feart.2021.600930 ◽

2021 ◽

Vol 9 ◽

Author(s):

Takuya Hasegawa ◽

Akira Nagano ◽

Keisuke Ariyoshi ◽

Toru Miyama ◽

Hiroyuki Matsumoto ◽

...

Keyword(s):

Sea Surface ◽

Slow Slip ◽

Slow Slip Events ◽

Plate Convergence ◽

Southeastern Coast ◽

Warm Core ◽

Slow Earthquakes ◽

The Relationship ◽

Interannual Scale

The relationship between sea surface height (SSH) and seawater density anomalies, which affects the pressure on the seafloor (PSF) anomalies off the southeastern coast of Hokkaido, Japan, was analyzed using the eddy-resolving spatial resolution ocean assimilation data of the JCOPE2M for the period 2001–2018. On an interannual (i.e., year-to-year) timescale, positive SSH anomalies of nearly 0.1 m appeared off the southeastern coast of Hokkaido, Japan, in 2007, associated with a warm-core ring (WCR), while stronger SSH anomalies (∼0.2 m) related to a stronger WCR occurred in 2016. The results show that the effects of such positive SSH anomalies on the PSF are almost canceled out by the effects of negative seawater density anomalies from the seafloor to the sea surface (SEP; steric effect on PSF) due to oceanic baroclinic structures related to the WCRs, especially in offshore regions with bottom depths greater than 1000 m. This means that oceanic isostasy is well established in deep offshore regions, compared with shallow coastal regions. To further verify the strength of the oceanic isostasy, oceanic isostasy anomalies (OIAs), which represent the barotropic component of SSH anomalies, are introduced and analyzed in this study. OIAs are defined as the sum of the SSH anomalies and SEP anomalies. Our results indicate that the effect of oceanic fluid changes due to SSH and seawater density anomalies (i.e., OIAs) on PSF changes cannot be neglected on an interannual timescale, although the amplitudes of the OIAs are nearly 10% of those of the SSH anomalies in the offshore regions. Therefore, to better estimate the interannual-scale PSF anomalies due to crustal deformation related to slow earthquakes including afterslips, long-term slow slip events, or plate convergence, the OIAs should be removed from the PSF anomalies.

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Dilation and compaction accompanying changes in slip velocity in clay-bearing fault gouges

10.5194/egusphere-egu21-8679 ◽

2021 ◽

Author(s):

Isabel Ashman ◽

Daniel Faulkner

Keyword(s):

Normal Stress ◽

Pore Pressure ◽

Volume Change ◽

Slip Velocity ◽

Fault Slip ◽

Slow Slip ◽

Volume Changes ◽

Effective Normal Stress ◽

Earthquake Nucleation ◽

Fault Gouges

Many natural fault cores comprise volumes of extremely fine, low permeability, clay-bearing fault rocks. Should these fault rocks undergo transient volume changes in response to changes in fault slip velocity, the subsequent pore pressure transients would produce significant fault weakening or strengthening, strongly affecting earthquake nucleation and possibly leading to episodic slow slip events. Dilatancy at slow slip velocity has previously been measured in quartz-rich gouges but little is known about gouge containing clay. In this work, the mechanical behaviour of synthetic quartz-kaolinite fault gouges and their volume response to velocity step changes were investigated in a suite of triaxial deformation experiments at effective normal stresses of 60MPa, 25MPa and 10MPa. Kaolinite content was varied from 0 to 100wt% and slip velocity was varied between 0.3 and 3 microns/s.Upon a 10-fold velocity increase or decrease, gouges of all kaolinite-quartz contents displayed measurable volume change transients. The results show the volume change transients are independent of effective normal stress but are sensitive to gouge kaolinite content. Peak dilation values did not occur in the pure quartz gouges, but rather in gouges containing 10wt% to 20wt% kaolinite. Above a kaolinite content of 10wt% to 20wt%, both dilation and compaction decreased with increasing gouge kaolinite content. At 25MPa effective normal stress, the normalised volume changes decreased from 0.1% to 0.06% at 10wt% to 100wt% kaolinite.&#160; The gouge mechanical behaviour shows that increasing the gouge kaolinite content decreases the gouge frictional strength and promotes more stable sliding, rather than earthquake slip. Increasing the effective normal stress slightly decreases the frictional strength, enhances the chance of earthquake nucleation, and has no discernible effect on the magnitude of the pore volume changes during slip velocity changes.Low permeabilities of clay-rich fault gouges, coupled with the observed volume change transients, could produce pore pressure fluctuations up to 10MPa in response to fault slip. This assumes no fluid escape from an isolated fault core. Where the permeability is finite, any pore pressure changes will be mediated by fluid influx into the gouge. Volume change transients could therefore be a significant factor in determining whether fault slip leads to earthquake nucleation or a dampened response, possibly resulting in episodic slow slip in low permeability fault rock volumes.

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