Seafloor Borehole Observatory Array for Monitoring Slow Slip Events in the Nankai Trough Seismogenic Zone

Subduction zones are where the largest earthquakes occur. In the past few decades, scientists have also discovered the presence of episodic aseismic slip, including slow slip events (SSEs), along most of the subduction zones. However, it is still unclear how these SSEs can influence megathrust earthquake ruptures. The Costa Rica subduction zone is a particularly interesting area because a SSE was recorded 6 months before the 2012 Mw7.6 earthquake in the Nicoya Peninsula, suggesting a potential stress transfer from the SSE to the earthquake slip zone. SSEs beneath the Nicoya Peninsula were also recorded both updip and downdip the seismogenic zone, making it a unique area to study the complex interaction between SSEs and earthquakes.As most of the shallow SSEs were recorded around the Nicoya Peninsula, we chose to start using a 1D planar fault embedded in a homogeneous elastic half-space, with different dipping angles following several geometric profiles of the subduction fault beneath the Nicoya Peninsula section of the Costa Rica margin. This 1D modelling study allows us to better investigate the interaction between shallow and deep SSEs and megathrust earthquakes with high numerical resolution and relatively short computation time. The model provides information on the long-term seismic history by reproducing the different stages of the seismic cycle (interseismic slip, shallow and deep episodic slow slip, and coseismic slip).We study the influence of the variation of numerical parameters and frictional properties on the recurrence interval, maximum slip velocity and cumulative slip of SSEs (both shallow and deep) and earthquakes and their interaction with each other. We then compare our results with GPS and seismic observations (i.e. cumulative slip, characteristic duration, moment rate, depth and size of the rupture, equivalent magnitude) to identify an optimal set of model parameters to understand the interaction between various modes of subduction fault deformation.

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Record by quartz veins of earthquakes and slow slip events

10.5194/egusphere-egu2020-5472 ◽

2020 ◽

Author(s):

Hugues Raimbourg ◽

Vincent Famin ◽

Kristijan Rajic ◽

Saskia Erdmann ◽

Benjamin Moris-Muttoni ◽

...

Keyword(s):

Trace Element ◽

Fluid Pressure ◽

Trace Element Content ◽

Element Content ◽

Seismogenic Zone ◽

Slow Slip ◽

Slow Slip Events ◽

Quartz Veins ◽

Temperature Conditions ◽

Montagne Noire

Veins that form contemporaneously with deformation are the best recorders of the fluids circulating in the depths of orogenic and subduction zones. We have analyzed syn-kinematic quartz veins from accretionary prisms (Shimanto Belt in Japan, Kodiak accretionary prism in Alaska) and tectonic nappes in collisional orogens (Flysch &#224; Helmintho&#239;des in the Alps, the southern domain of the variscan Montagne Noire), which formed at temperature conditions between 250 and 350&#176;C, i.e. spanning the downdip limit of large subduction earthquakes and the generation of slow slip events. In all geological domains, veins hosted in rocks with the lower temperature conditions (~250-300&#176;C) show quartz grains with crystallographic facets and growth rims. Cathodoluminescence (CL) imaging of these growth rims shows two different colors, a short-lived blue color and a brown one, attesting to cyclic variations in precipitation conditions. In contrast, veins hosted in rocks with the higher temperature conditions (~350&#176;C), show a homogeneous, CL-brown colored quartz, except for some very restricted domains of crack-seal structures of CL-blue quartz found in Japan, Kodiak and Montagne Noire. Based on laser ablation and electron microprobe mapping, the variations in CL colors appear correlated with the trace element content of quartz, the short-lived CL-blue being associated with the substitution of Si4+ by Al3++Li+/H+.Due to their ubiquitous presence in various settings, the variations in CL colors in the lower T range reflect a common, general process. We interpret these cyclic growth structures as a reflection of deformation/fracturing events, which triggered transient changes in (1) the fluid pressure through fluid flow and (2) the chemistry of the fluid due to enhanced reactivity of the fractured material. The CL-blue growth rims delineate zones where quartz growth was rapid and crystals incorporated a large proportion of Al and Li. Crystal growth continued at a lower pace after fluid pressure and composition evolved to equilibrium conditions, leading to the formation of CL-brown quartz with few substitutions of tetrahedral Si. The variations in fluid pressure fluctuated at values close to lithostatic conditions, as indicated by growth in cavities that remained open.The crack-seal microstructures have been interpreted as the result of slow-slip events near the base of the seismogenic zone (Fisher and Brantley, 2014; Ujiie et al., 2018). Our observations on quartz composition suggest that the quartz in crack-seal microstructures records episodic variation in fluid pressure and composition, similar to vein quartz at T<~300 &#176;C. In contrast to the cooler and shallower domain, the variations are significantly smaller, as recorded by the very limited extent of the CL-blue domains, and most if not all of the quartz growth occurred under constant physico-chemical conditions, including a near lithostatic fluid pressure.&#160;We conclude that quartz trace element content is a useful tool to track variations in fluid conditions. In particular, at seismogenic depths (i.e. near 250&#176;C), fluid pressure varies significantly around a lithostatic value. In contrast, deeper, near the base of the seismogenic zone where slow slip events occur (i.e. near 350&#176;C), the variations in fluid pressure conditions are smaller.

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Recurring and triggered slow-slip events near the trench at the Nankai Trough subduction megathrust

Science ◽

10.1126/science.aan3120 ◽

2017 ◽

Vol 356 (6343) ◽

pp. 1157-1160 ◽

Cited By ~ 107

Author(s):

Eiichiro Araki ◽

Demian M. Saffer ◽

Achim J. Kopf ◽

Laura M. Wallace ◽

Toshinori Kimura ◽

...

Keyword(s):

Nankai Trough ◽

Slow Slip ◽

Slow Slip Events

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Fluid pressure variations recorded by quartz vein geochemistry

10.5194/egusphere-egu21-10074 ◽

2021 ◽

Author(s):

Hugues Raimbourg ◽

Vincent Famin ◽

Kristijan Rajic ◽

Saskia Erdmann ◽

Benjamin Moris-Muttoni ◽

...

Keyword(s):

Trace Element ◽

Fluid Pressure ◽

Trace Element Content ◽

Element Content ◽

Seismogenic Zone ◽

Slow Slip ◽

Slow Slip Events ◽

Temperature Conditions ◽

Montagne Noire ◽

Lower Temperature

Veins that form contemporaneously with deformation are the best recorders of the fluids circulating in the depths of orogenic and subduction zones. We have analyzed syn-kinematic quartz veins from accretionary prisms (Shimanto Belt in Japan, Kodiak accretionary Complex in Alaska) and tectonic nappes in collisional orogens (Flysch &#224; Helmintho&#239;des in the Alps, southern nappes of the variscan Montagne Noire), which formed at temperature conditions between 250 and 350&#176;C, i.e. spanning the downdip limit of large subduction earthquakes and the generation of slow slip events. In all geological domains, veins hosted in rocks that have experienced the lower temperature conditions (~250-300&#176;C) show quartz grains with crystallographic facets and growth rims. Cathodoluminescence (CL) imaging of these growth rims shows two different colors, a short-lived blue color and a brown one, attesting to cyclic variations in precipitation conditions. In contrast, veins hosted in rocks that have experienced the higher temperature conditions (~350&#176;C), show a homogeneous, CL-brown colored quartz, except for some very restricted domains of crack-seal structures of CL-blue quartz found in Japan, Kodiak and Montagne Noire.Based on laser ablation analysis and electron microprobe mapping, variations in CL colors appear correlated with the trace element content of quartz. The highly luminescent quartz contains high concentrations of aluminum (Al) and lithium (Li), up to 3000 and 400 ppm, respectively. Variations in Al and Li correlate well, so that Li appears as the main charge&#8208;compensating cation for Si&#224;Al substitution.Due to their ubiquitous presence in various settings, the variations in CL colors in the lower temperature range reflect a common, general process. We interpret these cyclic growth structures as a result of deformation/fracturing events, which triggered transient changes in fluid pressure. The CL-blue growth rims delineate zones where quartz growth was rapid and crystals incorporated a large proportion of Al and Li. Crystal growth continued at lower pace after fluid pressure evolved to equilibrium conditions, leading to the formation of CL-brown quartz with fewer substitutions of tetrahedral Si. The variations in fluid pressure fluctuated at values close to lithostatic conditions, as indicated by growth in cavities that remained open.The crack-seal microstructures have been interpreted as the result of slow-slip events near the base of the seismogenic zone (Fisher and Brantley, 2014; Ujiie et al., 2018). Our observations on quartz composition suggest that the quartz in crack-seal microstructures records episodic variation in fluid pressure, similar to vein quartz at T<~300 &#176;C. In contrast to the cooler and shallower domain, the variations are significantly smaller, as recorded by the very limited extent of the CL-blue domains, and most if not all of the quartz growth occurred under constant physico-chemical conditions, including a near lithostatic fluid pressure.&#160;We conclude that quartz trace element content might be a useful tool to track variations in fluid conditions. In particular, at seismogenic depths (i.e. near 250&#176;C), fluid pressure varies significantly around a lithostatic value. In contrast, deeper, near the base of the seismogenic zone where slow slip events occur (i.e. near 350&#176;C), the variations in fluid pressure are smaller.

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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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Excitation of San Andreas tremors by thermal instabilities below the seismogenic zone

Science Advances ◽

10.1126/sciadv.abb2057 ◽

2020 ◽

Vol 6 (36) ◽

pp. eabb2057 ◽

Cited By ~ 1

Author(s):

Lifeng Wang ◽

Sylvain Barbot

Keyword(s):

Low Frequency ◽

Frictional Resistance ◽

Seismogenic Zone ◽

Slow Slip ◽

Slow Slip Events ◽

Tectonic Plates ◽

San Andreas ◽

Wide Range ◽

Shear Heating ◽

Increasing Temperature

The relative motion of tectonic plates is accommodated at boundary faults through slow and fast ruptures that encompass a wide range of source properties. Near the Parkfield segment of the San Andreas fault, low-frequency earthquakes and slow-slip events take place deeper than most seismicity, at temperature conditions typically associated with stable sliding. However, laboratory experiments indicate that the strength of granitic gouge decreases with increasing temperature above 350°C, providing a possible mechanism for weakening if temperature is to vary dynamically. Here, we argue that recurring low-frequency earthquakes and slow-slip transients at these depths may arise because of shear heating and the temperature dependence of frictional resistance. Recurring thermal instabilities can explain the recurrence pattern of the mid-crustal low-frequency earthquakes and their correlative slip distribution. Shear heating associated with slow slip is sufficient to generate pseudotachylyte veins in host rocks even when fault slip is dominantly aseismic.

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