Spatial changes in inclusion band spacing as an indicator of temporal changes in slow slip and tremor recurrence intervals

AbstractSlow slip and tremor (SST) downdip of the seismogenic zones may trigger megathrust earthquakes by frequently transferring stress to seismogenic zones. Geodetic observations have suggested that the recurrence intervals of slow slip decrease toward the next megathrust earthquake. However, temporal variations in the recurrence intervals of SST during megathrust earthquake cycles remain poorly understood because of the limited duration of geodetic and seismological monitoring of slow earthquakes. The quartz-filled, crack-seal shear veins in the subduction mélange deformed near the downdip limit of the seismogenic zone in warm-slab environments record cyclic changes in the inclusion band spacing in the range from 4 ± 1 to 65 ± 18 μm. The two-phase primary fluid inclusions in quartz between inclusion bands exhibit varying vapor/liquid ratios regardless of inclusion band spacing, suggesting a common occurrence of fast quartz sealing due to a rapid decrease in quartz solubility associated with a large fluid pressure reduction. A kinetic model of quartz precipitation, considering a large fluid pressure change and inclusion band spacing, indicates that the sealing time during a single crack-seal event cyclically decreased and increased in the range from 0.16 ± 0.04 to 2.7 ± 0.8 years, with one cycle lasting at least 27 ± 2 to 93 ± 5 years. The ranges of sealing time and duration of a cycle may be comparable to the recurrence intervals of SST and megathrust earthquakes, respectively. We suggest that the spatial change in inclusion band spacing is a potential geological indicator of temporal changes in SST recurrence intervals, particularly when large fluid pressure reduction occurs by brittle fracturing.

Download Full-text

Spatial changes in inclusion band spacing as an indicator of temporal changes in slow earthquake recurrence intervals

10.5194/egusphere-egu21-9339 ◽

2021 ◽

Author(s):

Naoki Nishiyama ◽

Kohtaro Ujiie ◽

Masayuki Kano

Keyword(s):

Fluid Pressure ◽

Cycle Duration ◽

Pressure Reduction ◽

Earthquake Recurrence ◽

Megathrust Earthquake ◽

Megathrust Earthquakes ◽

Slow Earthquake ◽

Slow Earthquakes ◽

Recurrence Intervals ◽

Band Spacing

Repeated slow earthquakes downdip of the seismogenic zones may trigger megathrust earthquakes by transferring stress to the seismogenic zones. Geodetic observations have suggested that the recurrence intervals of slow earthquakes decrease toward a next megathrust earthquake. However, the temporal variation in recurrence intervals of slow earthquakes during megathrust earthquake cycles remains poorly understood due to the limited duration of geodetic and seismological monitoring of slow earthquakes. The quartz-filled, crack-seal shear veins in the subduction m&#233;lange deformed near the downdip limit of seismogenic zone in warm-slab environments record the cyclic changes in the inclusion band spacing in the range of 5&#8211;65 &#956;m. The two-phase primary fluid inclusions in quartz between inclusion bands show various vapor/liquid ratios regardless of inclusion band spacing, suggesting a common occurrence of fast quartz sealing due to a rapid decrease in quartz solubility associated with a large fluid pressure reduction. A kinetic model of quartz precipitation, considering a large fluid pressure change and inclusion band spacings, indicates that the sealing time during a single crack-seal event cyclically decreased and increased in the range of 0.2&#8211;2.7 years, with minimum one cycle duration estimated to be 31&#8211;93 years. The ranges of sealing time and one cycle duration may be comparable to the recurrence intervals of slow earthquakes and megathrust earthquakes, respectively. We suggest that the spatial change in the inclusion band spacing is a potential geological indicator of the temporal changes in slow earthquake recurrence intervals, particularly when large fluid pressure reduction occurred by brittle fracturing.

Download Full-text

Episodic fluid pressure cycling controls earthquake sequences on subduction megathrusts

10.5194/egusphere-egu21-13728 ◽

2021 ◽

Author(s):

Luca Dal Zilio ◽

Taras Gerya

Keyword(s):

Fluid Flow ◽

Finite Difference Methods ◽

Fluid Pressure ◽

Seismogenic Zone ◽

Slow Slip ◽

Aseismic Slip ◽

Earthquake Physics ◽

Megathrust Earthquakes ◽

Pressure Cycling ◽

Crustal Stresses

A major goal in earthquake physics is to derive a constitutive framework for fault slip that captures the dependence of friction on lithology, sliding velocity, temperature, and pore fluid pressure. Here, we present a newly-developed two-phase flow numerical model &#8212; which couples solid rock deformation and pervasive fluid flow &#8212; to show how crustal stresses and fluid pressures within subducting megathrust evolve before and during slow slip and fast events. This unified 2D numerical framework couples inertial mechanical deformation and fluid flow by using finite difference methods, marker-in-cell technique, and poro-visco-elasto-plastic rheology. An adaptive time stepping allows the correct resolution of both long- and short-time scales, ranging from years to milliseconds during the dynamic propagation of dynamic rupture.We investigate how permeability and its spatial distribution control the interseismic coupling along the megathrust interface, the interplay between seismic and aseismic slip, and the nucleation of large earthquakes. While a constant permeability leads to more regular seismic cycles, a depth dependent permeability contributes substantially to the development of two distinct megathrust zones: a shallow, locked seismogenic zone and a deep, narrow aseismic segment characterized by slow-slip events. Furthermore, we show that without requiring any specific friction law, our models reveal that permeability, episodic stress transfer and fluid pressure cycling control the predominant slip mode along the subduction megathrust. Furthermore, we analyze how rate dependent strength and dilatation affect rupture propagation and arrest. Our preliminary results show that fluid-solid poro-visco-elasto-plastic coupling behaves similarly to rate- and state-dependent friction. In this context, fluid pressure plays the role of state parameter whose time evolution is governed by: (i) the short-term elasto-plastic collapse of pores inside faults during the rupture (coseismic self-pressurization of faults) and (ii) the long-term pore-pressure diffusion from the faults into surrounding rocks (post- and interseismic relaxation of fluid pressure). This newly-developed numerical framework contributes to improve our understanding of the physical mechanisms underlying large megathrust earthquakes, and demonstrate that fluid play a key role in controlling the interplay between seismic and aseismic slip.

Download Full-text

Episodic fluid pressure cycling controls the interplay between Slow Slip Events and Large Megathrust Earthquakes

10.5194/egusphere-egu2020-17557 ◽

2020 ◽

Author(s):

Claudio Petrini ◽

Luca Dal Zilio ◽

Taras Gerya

Keyword(s):

Fluid Flow ◽

Subduction Zones ◽

Finite Difference Methods ◽

Fluid Pressure ◽

Slow Slip ◽

Aseismic Slip ◽

Slow Slip Events ◽

Megathrust Earthquakes ◽

Pressure Cycling ◽

Crustal Stresses

Slow slip events (SSEs) are part of a spectrum of aseismic processes that relieve tectonic stress on faults. Their occurrence in subduction zones have been suggested to trigger megathrust earthquakes due to perturbations in fluid pressure. However, examples to date have been poorly recorded and physical observations of temporal fluid pressure fluctuations through slow slip cycles remain elusive. Here, we use a newly developed two-phase flow numerical model &#8212; which couples solid rock deformation and pervasive fluid flow &#8212; to show how crustal stresses and fluid pressures within subducting megathrust evolve before and during slow slip and regular events. This unified 2D numerical framework couples inertial mechanical deformation and fluid flow by using finite difference methods, marker-in-cell technique, and poro-visco-elasto-plastic rheologies. Furthermore, an adaptive time stepping allows the correct resolution of both long- and short-time scales, ranging from years to milliseconds during the dynamic propagation of earthquake rupture.Here we show how permeability and its spatial distribution control the degree of locking along the megathrust interface and the interplay between seismic and aseismic slip. While a constant permeability leads to more regular seismic cycles, a depth dependent permeability contributes substantially to the development of two distinct megathrust zones: a shallow, locked seismogenic zone and a deep, narrow aseismic segment characterized by SSEs. Furthermore, we show that without requiring any specific friction law, our model shows that permeability, episodic stress transfer and fluid pressure cycling control the predominant slip mode along the subduction megathrust. Specifically, we find that the up-dip propagation of episodic SSEs systematically decreases the fault strength due to a continuous accumulation and release of fluid pressure within overpressured subducting interface, thus affecting the timing of large megathrust earthquakes. These results contribute to improve our understanding of the physical driving forces underlying the interplay between seismic and aseismic slip, and demonstrate that slow slip events may prove useful for short-term earthquake forecasts.

Download Full-text

Effects of episodic slow slip on seismicity and stress near a subduction-zone megathrust

Nature Communications ◽

10.1038/s41467-021-27453-8 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Saeko Kita ◽

Heidi Houston ◽

Suguru Yabe ◽

Sachiko Tanaka ◽

Youichi Asano ◽

...

Keyword(s):

Subduction Zones ◽

Fluid Pressure ◽

Plate Boundary ◽

Slow Slip ◽

Plate Interface ◽

B Values ◽

Megathrust Earthquakes ◽

Cyclic Processes ◽

Stress Orientations ◽

Oceanic Slab

AbstractSlow slip phenomena deep in subduction zones reveal cyclic processes downdip of locked megathrusts. Here we analyze seismicity within a subducting oceanic slab, spanning ~50 major deep slow slip with tremor episodes over 17 years. Changes in rate, b-values, and stress orientations of in-slab seismicity are temporally associated with the episodes. Furthermore, although stress orientations in the slab below these slow slips may rotate slightly, in-slab orientations 20–50 km updip from there rotate farther, suggesting that previously-unrecognized transient slow slip occurs on the plate interface updip. We infer that fluid pressure propagates from slab to interface, promoting episodes of slow slip, which break mineral seals, allowing the pressure to propagate tens of km further updip along the interface where it promotes transient slow slips. The proposed methodology, based primarily on in-slab seismicity, may help monitor plate boundary conditions and slow slip phenomena, which can signal the beginning stages of megathrust earthquakes.

Download Full-text

Stress state along the western Nankai Trough subduction zone inferred from b-values, long-term slow-slip events, and low-frequency earthquakes

Earth Planets and Space ◽

10.1186/s40623-020-1130-7 ◽

2020 ◽

Vol 72 (1) ◽

Cited By ~ 1

Author(s):

Keita Chiba

Keyword(s):

Low Frequency ◽

Value Distribution ◽

Focal Region ◽

Slow Slip ◽

Slow Slip Events ◽

Megathrust Earthquakes ◽

Source Regions ◽

Slow Earthquakes ◽

Subducting Plate

AbstractThe b-value of the Gutenberg–Richter law represents the ratio of earthquake magnitude to frequency of occurrence and is inversely proportional to differential stress. Repeating long-term slow-slip events (SSEs) and low-frequency earthquakes (LFEs) occur at subducting plate interfaces and have stress-dependent characteristics near the interface. In this study, a comprehensive regional b-value distribution is produced for the western Nankai Trough region, which highlights the relationship between b-values, SSEs, and LFEs. b-values vary along the strike direction of the subducting plate and are significantly lower $$ \left( {b \sim 0.6} \right) $$b∼0.6 in central Shikoku district than elsewhere, where LFEs frequently occur. However, b-values in the source regions of other LFEs are moderate to high. These findings imply that b-values in the focal region are controlled by more than the LFE source process; indeed, if this source process were solely responsible, then high b-values would be expected. Meanwhile, the $$ V_{P} /V_{S} $$VP/VS and QP around the plate interface in central Shikoku estimated from seismic velocity and attenuation structure are smaller and larger than those in other regions with LFEs, respectively. SSEs with the migration toward central Shikoku also occurred during the analysis period, suggesting significant accumulation of shear stresses in the focal region, which reduced the b-values. These findings suggest that the spatial distributions of b-values are influenced by complicated stress and shear strength perturbations caused by SSEs and LFEs. On the other hand, the b-values in the region that underwent the greatest slip during the 1946 Nankai earthquake are not necessarily low, although the area covered by the b-value distribution is small owing to the lack of events on the updip side. Whereas the asperity areas of huge earthquakes are characterized by low b-values, the b-value distribution in the Nankai megathrust area is more complicated. It is considered that slow earthquakes, including SSEs and LFEs, are related to megathrust earthquakes via stress transfer from slow earthquakes to adjacent megathrust source regions. A unified analysis of b-values in the source regions of slow and megathrust earthquakes may be required to make precise estimates of the seismic hazard produced by a megathrust event.

Download Full-text

Fault zone heterogeneities explain depth-dependent pattern and evolution of slow earthquakes in Cascadia

Nature Communications ◽

10.1038/s41467-021-22232-x ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Yingdi Luo ◽

Zhen Liu

Keyword(s):

Pore Pressure ◽

Fault Zone ◽

Cascadia Subduction Zone ◽

Slow Slip ◽

Slow Slip Events ◽

Close Link ◽

Megathrust Earthquakes ◽

Effective Normal Stress ◽

Slow Earthquakes ◽

Rate And State Friction

AbstractSlow earthquakes including tremor and slow-slip events are recent additions to the conventional earthquake family and have a close link to megathrust earthquakes. Slow earthquakes along the Cascadia subduction zone display a diverse behavior at different spatiotemporal scales and an intriguing increase of events frequency with depth. However, what causes such variability, especially the depth-dependent behavior is not well understood. Here we build on a heterogeneous asperities-in-matrix fault model that incorporates differential pore pressure in a rate-and-state friction framework to investigate the underlying processes of the observed episodic tremor and slow-slip (ETS) variability. We find that the variations of effective normal stress (pore pressure) is one important factor in controlling ETS behavior. Our model reproduces the full complexity of ETS patterns and the depth-frequency scaling that agree quantitatively well with observations, suggesting that fault zone heterogeneities can be one viable mechanism to explain a broad spectrum of transient fault behaviors.

Download Full-text

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.

Download Full-text