scholarly journals Variations of fluid pressure within the subducting oceanic crust and slow earthquakes

2010 ◽  
Vol 37 (14) ◽  
pp. n/a-n/a ◽  
Author(s):  
Aitaro Kato ◽  
Takashi Iidaka ◽  
Ryoya Ikuta ◽  
Yasuhiro Yoshida ◽  
Kei Katsumata ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Fluid Pressure ◽  
Slow Earthquakes

scholarly journals Eclogitization of the Subducted Oceanic Crust and Its Implications for the Mechanism of Slow Earthquakes

2017 ◽  
Vol 44 (24) ◽  
Author(s):  
Xinyang Wang ◽  
Dapeng Zhao ◽  
Haruhiko Suzuki ◽  
Jiabiao Li ◽  
Aiguo Ruan
Keyword(s):  
Oceanic Crust ◽  
Slow Earthquakes ◽  
Subducted Oceanic Crust

Underplating altered oceanic crust: Insights from numerical modelling

2021 ◽  
Author(s):  
Zoe Braden ◽  
Jonas B. Ruh ◽  
Whitney M. Behr
Keyword(s):  
Numerical Modelling ◽  
Oceanic Crust ◽  
Fluid Pressure ◽  
Geothermal Gradient ◽  
Pore Fluid ◽  
Surface Erosion ◽  
Accretionary Wedge ◽  
Pore Fluid Pressure ◽  
Mafic Rocks

<p>Observations of several active shallow subduction megathrusts suggest that they are localized as décollements within sedimentary sequences or at the contact between sedimentary layers and the underlying mafic oceanic crust.  Exhumed accretionary complexes from a range of subduction depths, however, preserve underplated mafic slivers, which indicate that megathrust faults can occasionally develop within the mafic oceanic crustal column. The incorporation of mafic rocks into the subduction interface shear zone has the potential to influence both long-term subduction dynamics and short-term seismic and transient slip behaviour, but the processes and conditions that favour localisation of the megathrust into deeper oceanic crustal levels are poorly understood.</p><p>In this work, we use visco-elasto-plastic numerical modelling to explore the long-term (million year) factors influencing the incorporation of mafic volcanic rocks into the subduction interface and accretionary wedge through underplating. We focus on the potential importance of oceanic seafloor alteration in facilitating oceanic crustal weakening, which is implemented through a temperature-dependent pore-fluid pressure ratio (lambda = 0.90-0.99 between 160 and 300oC). We then examine the underplating response to changes in sediment thickness, geothermal gradient, sediment fluid pressure, and surface erosion rates. Our results indicate that a thinner incoming sediment package and a lower geothermal gradient cause oceanic crustal underplating to initiate deeper beneath the backstop (overriding plate) compared to thicker incoming sediment and a higher geothermal gradient. Relative pore fluid pressure differences between sediments and altered oceanic crust control the amount of altered oceanic crust that is underplated, as well as the location of underplating beneath the backstop or accretionary wedge. When sediments on top of the altered oceanic crust have the same fluid pressure as the altered oceanic crust, no oceanic crustal underplating occurs. Modelling results are also compared to exhumed subduction complexes to examine the amount and distribution of underplated mafic rocks.</p>

scholarly journals 3-D thermal regime and dehydration processes around the regions of slow earthquakes along the Ryukyu Trench

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Nobuaki Suenaga ◽  
Shoichi Yoshioka ◽  
Yingfeng Ji
Keyword(s):  
Phase Transformations ◽  
Oceanic Crust ◽  
Thermal Regime ◽  
Mantle Wedge ◽  
Plate Interface ◽  
Okinawa Island ◽  
Hydrous Minerals ◽  
Ryukyu Trench ◽  
Temperature Range ◽  
Slow Earthquakes

AbstractSeveral interplate seismic events, such as short-term slow slip events (S-SSEs) and low-frequency earthquakes (LFEs), have been identified in the Ryukyu Trench, southwestern Japan. As one of the specific characteristics of this seismicity, the depths at which S-SSEs occur at the plate interface beneath Okinawa Island are approximately 5–10 km shallower than those beneath the Yaeyama Islands. To elucidate the cause of this difference in depth, we constructed a three-dimensional, Cartesian thermomechanical subduction model and applied the subduction history of the Philippine Sea (PHS) plate in the model region. As a result, the interplate temperatures at which S-SSEs take place were estimated to range from 350 to 450 °C beneath Okinawa Island and from 500 to 600 °C beneath the Yaeyama Islands. The former temperature range is consistent with previous thermal modelling studies for the occurrence of slow earthquakes, but the latter temperature range is by approximately 150 °C higher than the former. Therefore, explaining how the depth difference in S-SSEs could be caused from the aspect of only the thermal regime is difficult. Using phase diagrams for hydrous minerals in the oceanic crust and mantle wedge, we also estimated the water content distribution on and above the plate interface of the PHS plate. Near the S-SSE fault planes, almost the same amount of dehydration associated with phase transformations of hydrous minerals from blueschist to amphibolite and from amphibolite to amphibole eclogite within the oceanic crust were inferred along Okinawa Island and the Yaeyama Islands, respectively. On the other hand, the phase transformations within the mantle wedge were inferred only beneath the Yaeyama Islands, whereas no specific phase transformation was inferred beneath Okinawa Island around the S-SSE occurrence region. Therefore, we conclude that dehydrated fluid derived from the oceanic crust at the plate interface would play a key role in the occurrence of S-SSEs.

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

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

<p>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 mélange 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 5–65 μm. 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 0.2–2.7 years, with minimum one cycle duration estimated to be 31–93 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.</p>

Episodic stress and fluid pressure cycling in subducting oceanic crust during slow slip

2019 ◽  
Vol 12 (6) ◽  
pp. 475-481 ◽  
Author(s):  
E. Warren-Smith ◽  
B. Fry ◽  
L. Wallace ◽  
E. Chon ◽  
S. Henrys ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Fluid Pressure ◽  
Slow Slip ◽  
Pressure Cycling ◽  
Episodic Stress

scholarly journals Fluid-controlled deformation in blueschist-facies conditions: plastic vs brittle behaviour in a brecciated mylonite (Voltri Massif, Western Alps, Italy)

2017 ◽  
Vol 155 (2) ◽  
pp. 335-355 ◽  
Author(s):  
C. MALATESTA ◽  
L. FEDERICO ◽  
L. CRISPINI ◽  
G. CAPPONI
Keyword(s):  
High Pressure ◽  
Fluid Pressure ◽  
Western Alps ◽  
Pore Fluid ◽  
Ductile Deformation ◽  
Pore Fluid Pressure ◽  
Plate Interface ◽  
Rock Interaction ◽  
Field Evidence ◽  
Slow Earthquakes

AbstractA blueschist-facies mylonite crops out between two high-pressure tectono-metamorphic oceanic units of the Ligurian Western Alps (NW Italy). This mylonitic metabasite is made up of alternating layers with different grain size and proportions of blueschist-facies minerals.The mylonitic foliation formed at metamorphic conditions of T = 220–310 °C and P = 6.5–10 kbar. The mylonite shows various superposed structures: (i) intrafoliar and similar folds; (ii) chocolate-tablet foliation boudinage; (iii) veins; (iv) breccia.The occurrence of comparable mineral assemblages along the foliation, in boudin necks, in veins and in breccia cement suggests that the transition from ductile deformation (folds) to brittle deformation (veining and breccia), passing through a brittle–ductile regime (foliation boudinage), occurred gradually, without a substantial change in mineral assemblage and therefore in the overall P–T metamorphic conditions (blueschist-facies).A strong fluid–rock interaction was associated with all the deformative events affecting the rock: the mylonite shows an enrichment in incompatible elements (i.e. As and Sb), suggesting an input of fluids, released by adjacent high-pressure metasedimentary rocks, during ductile deformation. The following fracturing was probably enhanced by brittle instabilities arising from strain and pore-fluid pressure partitioning between adjacent domains, without further external fluid input.Fluids were therefore fixed inside the rock during mylonitization and later released into a dense fracture mesh that allowed them to migrate through the mylonitic horizon close to the plate interface.We finally propose that the fracture mesh might represent the field evidence of past episodic tremors or ‘slow earthquakes’ triggered by high pore-fluid pressure.

Episodic stress tensor and fluid pressure cycling in subducting oceanic crust during Northern Hikurangi slow slip events

2020 ◽  
Author(s):  
Emily Warren-Smith ◽  
Bill Fry ◽  
Laura Wallace ◽  
Enrique Chon ◽  
Stuart Henrys ◽  
...  
Keyword(s):  
Shear Zone ◽  
Oceanic Crust ◽  
Subduction Zones ◽  
Fluid Pressure ◽  
Fluid Migration ◽  
Ocean Bottom ◽  
Slow Slip ◽  
Interface Shear ◽  
Slow Slip Events ◽  
Fluid Reservoir

<p><span>The occurrence of slow slip events (SSEs) in subduction zones has been proposed to be linked to the presence of, and fluctuations in near-lithostatic fluid pressures (P</span><sub><span>f</span></sub><span>) within the megathrust shear zone and subducting oceanic crust. In particular, the 'fault-valve' model is commonly used to describe occasional, repeated breaching of a low-permeability interface shear zone barrier, which caps an overpressured hydrothermal fluid reservoir. In this model, a precursory increase in fluid pressure may therefore be anticipated to precede megathrust rupture. Resulting activation of fractures during slip opens permeable pathways for fluid migration and fluid pressure decreases once more, until the system becomes sealed and overpressure can re-accumulate. While the priming conditions for cyclical valving behaviour have been observed at subduction zones globally, and evidence for post-megathrust rupture drainage exists, physical observations of precursory fluid pressure increases, and subsequent decreases, particularly within the subducting slab where hydrothermal fluids are sourced, remain elusive. </span></p><p><span>Here we use earthquake focal mechanisms recorded on an ocean-bottom seismic network to identify changes in the stress tensor within subducting oceanic crust during four SSEs in New Zealand’s Northern Hikurangi subduction zone. We show that the stress, or shape ratio, which describes the relative magnitudes of the principal compressive stress axes, shows repeated decreases prior to, and rapid increases during the occurrence of geodetically documented SSEs. We propose that these changes represent precursory accumulation and subsequent release of fluid pressure within overpressured subducting oceanic crust via a ‘valving’ model for megathrust slip behaviour. Our observations indicate that the timing of slow slip events on subduction megathrusts may be controlled by cyclical accumulation of fluid pressure within subducting oceanic crust.</span></p><p><span>Our model is further supported by observations of seismicity preceding a large SSE in the northern Hikurangi Margin in 2019, captured by ocean-bottom seismometer</span><span>s</span><span> and </span><span>absolute </span><span>pressure </span><span>recorders.</span> <span>O</span><span>bservations of microseismicity </span><span>during this period </span><span>indicate that a stress state conducive to vertical fluid flow was present in the downgoing plate prior to SSE initiation, before subsequently returning to a</span><span> down-dip</span><span> extensional state following the SSE. We propose this precursory seismicity is indicative of fluid migration towards the interface shear zone from the lower plate fluid reservoir, which may have helped triggering slip on the megathrust. </span></p><p><span>We also present preliminary results of a moment tensor study to investigate spatial and temporal patterns in earthquake source properties in SSE regions along the Hikurangi Margin. In particular, earthquakes near Porangahau – a region susceptible to dynamic triggering of tremor and where </span><span>shallow </span><span>SSEs occur every 5 years or so – exhibit distinctly lower double couple components than elsewhere along the margin. We </span><span>attribute this to elevated fluid pressures within the crust here, which is consistent with recent observations of high seismic reflectivity from an autocorrelation study. Such high fluid pressure may control the broad range of seismic and aseismic phenomena observed at Porangahau. </span></p>

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

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Naoki Nishiyama ◽  
Kohtaro Ujiie ◽  
Masayuki Kano
Keyword(s):  
Fluid Pressure ◽  
Temporal Changes ◽  
Pressure Reduction ◽  
Slow Slip ◽  
Megathrust Earthquake ◽  
Megathrust Earthquakes ◽  
Slow Earthquakes ◽  
Recurrence Intervals ◽  
Band Spacing ◽  
Cyclic Changes

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.

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