Estimation of frictional properties and slip evolution on a long-term slow slip event fault with the ensemble Kalman filter: numerical experiments

2019 ◽  
Vol 219 (3) ◽  
pp. 2074-2096 ◽  
Author(s):  
Kazuro Hirahara ◽  
Kento Nishikiori
Keyword(s):  
Surface Displacement ◽  
Slip Rate ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Actual Distribution ◽  
Frictional Properties ◽  
Data Analyses ◽  
Bungo Channel ◽  
Megathrust Faults ◽  
Gnss Data

Summary A variety of slow slip events at subduction zones have been observed. They can be stress meters for monitoring the stress state of megathrust faults during their earthquake cycles. In this study, we focus on long-term slow slip events (LSSEs) recurring at downdip portions of megathrust faults among such slow earthquakes. Data analyses and simulation studies of LSSEs have so far been executed independently. In atmosphere and ocean sciences, data assimilations that optimally combine data analyses and simulation studies have been developed. We develop a method for estimating frictional properties and monitoring slip evolution on an LSSE fault, with a sequential data assimilation method, the ensemble Kalman filter (EnKF). We executed numerical twin experiments for the Bungo Channel LSSE fault in southwest Japan to validate the method. First, based on a rate- and state-dependent friction law, we set a rate-weakening circular LSSE patch on the rate-strengthening flat plate interface, whose critical nucleation size is larger than that of the patch, and reproduced the observed Bungo Channel LSSEs with recurrence times of approximately 7 yr and slip durations of 1 yr. Then, we synthesized the observed data of surface displacement rates at uniformly distributed stations with noises from the simulated slip model. Using our EnKF method, we successfully estimated the frictional parameters and the slip rate evolution after a few cycles. Secondly, we considered the effect of the megathrust fault existing in the updip portion of the LSSE fault, as revealed by kinematic inversion studies of Global Navigation Satellite System (GNSS) data and added this locked region with a slip deficit rate in the model. We estimated the slip rate on the locked region only kinematically, but the quasi-dynamic equation of motion in each LSSE fault cell includes the stress term arising from the locked region. Based on this model, we synthesized the observed surface displacement rate data for the actual distribution of GNSS stations and executed EnKF estimations including the slip rate on the locked region. The slip rate on the locked region could be quickly retrieved. Even for the actual distribution of GNSS stations, we could successfully estimate frictional parameters and slip evolution on the LSSE fault. Thus, our twin numerical experiments showed the validity of our EnKF method, although we need further studies for actual GNSS data analyses.

scholarly journals Spatiotemporal slip distributions associated with the 2018–2019 Bungo Channel long-term slow slip event inverted from GNSS data

2022 ◽  
Vol 12 (1) ◽  
Author(s):  
Yukinari Seshimo ◽  
Shoichi Yoshioka
Keyword(s):  
Time Series Data ◽  
Series Data ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Bungo Channel ◽  
Slip Event ◽  
The Moment ◽  
Gnss Data ◽  
Gnss Time Series

AbstractLong-term slow slip events (L-SSEs) have repeatedly occurred beneath the Bungo Channel in southwestern Japan with durations of several months to a couple of years, with a recurrence interval of approximately 6 years. We estimated the spatiotemporal slip distributions of the 2018–2019 Bungo Channel L-SSE by inverting processed GNSS time series data. This event was divided into two subevents, with the first on the southwest side of the Bungo Channel from 2018.3 to 2018.7 and the second beneath the Bungo Channel from 2018.8 to 2019.4. Tectonic tremors became active on the downdip side of the L-SSE occurrence region when large slow slips took place beneath the Bungo Channel. Compared with the previous Bungo Channel L-SSEs, this spatiotemporal slip pattern and amount were similar to those of the 2002–2004 L-SSE. However, the slip expanded in the northeast and southwest directions in the latter half of the second subevent. The maximum amount of slip, the maximum slip velocity, the total released seismic moment, and the moment magnitude of the 2018–2019 L-SSE were estimated to be 28 cm, 54 cm/year, $$4.4 \times 10^{19}$$ 4.4 × 10 19 Nm, and 7.0, respectively, all of which were the largest among the 1996–1998, 2002–2004, 2009–2011, and 2018–2019 L-SSEs.

scholarly journals The role of effective normal stress, frictional properties, and convergence rates in characteristics of simulated slow slip events

2015 ◽  
Vol 42 (4) ◽  
pp. 1061-1067 ◽  
Author(s):  
W. David Watkins ◽  
Harmony V. Colella ◽  
Michael R. Brudzinski ◽  
Keith B. Richards-Dinger ◽  
James H. Dieterich
Keyword(s):  
Normal Stress ◽  
Convergence Rates ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Frictional Properties ◽  
Effective Normal Stress

scholarly journals Slip-rate-dependent friction as a universal mechanism for slow slip events

2020 ◽  
Vol 13 (10) ◽  
pp. 705-710
Author(s):  
Kyungjae Im ◽  
Demian Saffer ◽  
Chris Marone ◽  
Jean-Philippe Avouac
Keyword(s):  
Slip Rate ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Rate Dependent ◽  
Universal Mechanism

scholarly journals Slow slip events are regular earthquakes

2021 ◽  
Author(s):  
Huihui Weng
Keyword(s):  
Wave Speed ◽  
Physical Mechanism ◽  
Three Dimensional ◽  
Slip Rate ◽  
Slow Slip ◽  
S Wave ◽  
Slow Slip Events ◽  
Fundamental Model ◽  
Wave Effects ◽  
Dynamic Wave

Abstract Slow slip events usually occur downdip of seismogenic zones in subduction megathrusts and crustal faults, with rupture speeds much slower than earthquakes. The empirical moment-duration scaling relation can help constrain the physical mechanism of slow slip events, yet it is still debated whether this scaling is linear or cubic and a fundamental model unifying slow slip events and earthquakes is still lacking. Here I present numerical simulations that show that slow slip events are regular earthquakes with negligible dynamic-wave effects. A continuum of rupture speeds, from arbitrarily-slow speeds up to the S-wave speed, is primarily controlled by the stress drop and a transition slip rate above which the fault friction transitions from rate-weakening behaviour to rate-strengthening behaviour. This continuum includes tsunami earthquakes, whose rupture speeds are about one-third of the S-wave speed. These numerical simulation results are predicted by the three-dimensional theory of dynamic fracture mechanics of elongated ruptures. This fundamental model unifies slow slip events and earthquakes, reconciles the observed moment-duration scaling relations, and opens new avenues for understanding earthquakes through investigations of the kinematics and dynamics of frequently occurring slow slip events.

scholarly journals Do slow slip events trigger large and great megathrust earthquakes?

2018 ◽  
Vol 4 (10) ◽  
pp. eaat8472 ◽  
Author(s):  
N. Voss ◽  
T. H. Dixon ◽  
Z. Liu ◽  
R. Malservisi ◽  
M. Protti ◽  
...  
Keyword(s):  
Costa Rica ◽  
Power Law ◽  
Slip Rate ◽  
Failure Stress ◽  
Slow Slip ◽  
Short Term ◽  
Slow Slip Events ◽  
Megathrust Earthquakes ◽  
Coulomb Failure ◽  
Earthquake Nucleation

Slow slip events have been suggested to trigger subduction earthquakes. However, examples to date have been poorly recorded, occurring offshore, where data are sparse. Better understanding of slow slip events and their influence on subsequent earthquakes is critical for hazard forecasts. We analyze a well-recorded event beginning 6 months before the 2012 Mw (moment magnitude) 7.6 earthquake in Costa Rica. The event migrates to the eventual megathrust rupture. Peak slip rate reached a maximum of 5 mm/day, 43 days before the earthquake, remaining high until the earthquake. However, changes in Mohr-Coulomb failure stress at the hypocenter were small (0.1 bar). Our data contradict models of earthquake nucleation that involve power law acceleration of slip and foreshocks. Slow slip events may prove useful for short-term earthquake forecasts.

Cycles of seismic and aseicmic slip recorded in faulted sediments under shallow burial conditions

2021 ◽  
Author(s):  
Mattia Pizzati ◽  
Fabrizio Balsamo ◽  
Fabrizio Storti
Keyword(s):  
Grain Size ◽  
Fractal Dimension ◽  
Fault Zone ◽  
Slip Rate ◽  
Preferred Orientation ◽  
High Porosity ◽  
Slow Slip ◽  
Deformation Bands ◽  
Slow Slip Events ◽  
Mean Grain Size

<p>Valuable information concerning the seismic cycle are mainly provided by the study of exposed fossil subduction-accretionary complexes and by coring and probing through present-day active major plate boundary interfaces. Subduction zone investigation and monitoring allowed to comprehend the mechanics of thrust-related faulting and to discern seismic events with different slip rate (coseismic events, slow slip events and tremor). While subduction zones received particular attention especially following the M<sub>w</sub> 9 Tohoku-Oki earthquake in Japan, relatively small-scale extensional faults affecting the uppermost portion of seismogenic zone of the Earth’s crust are still less studied.</p><p>Here, we present a field and laboratory study of meso-scale structures recorded within the fault core of an extensional fault zone (Rocca di Neto fault, offset < 100 m) affecting Pleistocene siliciclastic sediments in the Crotone Basin, Calabria, Southern Italy. Due to shallow burial conditions experienced by deformed sediments (< 400-500 m), the fault zone structure is characterised by deformation features typical of high-porosity granular rocks, with extensive occurrence of deformation bands, subsidiary faults and gouges. The 1 m-thick fault core displays a complex network of mutually cross-cutting black gouges and deformation bands developed in foliated sand. Some black gouges have straight pattern parallel to the master fault surface, while others are displaced and dragged along the deformation bands (mm-offset). Black gouges, previously interpreted as coseismic events due to moderate to high-temperature mineral assemblage, are characterised by cm-offset and extreme grain comminution via severe cataclasis (mean grain size of 20-30 μm and fractal dimension from 3.0 to 3.3); clast preferred orientation is almost parallel to the gouge outer boundaries, thus resulting in a well-developed foliation. Deformation bands are organised in two conjugate sets and display moderate to intense cataclasis depending on the accommodated displacement (mean grain size of 80-170 μm and fractal dimension from 2.4 to 2.8), with preferred orientation of clasts describing an angle of 30-45° from the band surface. Within deformation bands the foliation is less defined compared to black gouges. At the intersections between gouges and deformation bands, the resulting tectonic fabric is given by the superposition of different deformation events overprinting the original one.</p><p>The difference in grain size distribution, fractal dimension, clast shape preferred orientation (i.e., foliation) and mineral composition between black gouges and deformation bands supports the hypothesis of different slip rates causing their development. In particular, black gouges are interpreted to develop during coseismic slip (~0.1-1 m/s), while deformation bands formed during interseismic intervals (slip rate from nm/s to μm/s). The cross-cutting relationship between gouges and deformation bands, combined with the overprinting of different tectonic fabrics along the intersections, suggests they formed as a result of repeating coseismic (fast slip) and aseismic (slow slip) events occurring at shallow burial-near surface conditions. This feature could be a key point to evaluate the deformation style (fast vs slow slip) and to estimate the potential seismic hazard of superficial faults affecting high-porosity sediments.</p>

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