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.

A New Approach to Clarify Slow Earthquake Source Regions: Multi-band Receiver Function Analysis Including Local Deep-focus Events

2020 ◽  
Author(s):  
Yasunori Sawaki ◽  
Yoshihiro Ito ◽  
Kazuaki Ohta ◽  
Takuo Shibutani ◽  
Tomotaka Iwata
Keyword(s):  
Mantle Wedge ◽  
Receiver Function ◽  
Short Term ◽  
Plate Interface ◽  
Slow Earthquake ◽  
Source Regions ◽  
Slow Earthquakes ◽  
Deep Focus ◽  
Teleseismic Events ◽  
Multi Band

<p>Slow earthquakes play important roles in the occurrence of megathrust earthquakes in subduction zones. An increasing number of seismic networks have contributed to significant findings and the detection of slow earthquake activities; however, it is still unclear what sort of seismological structures exhibits each slow earthquake activity. We have developed the multi-band receiver function (RF) method, in which the RFs are composed of different higher-frequency contents. We, here, reveal smaller-scale structures from the RFs from local deep-focus earthquakes around the Philippine Sea plate boundary in Southwestern Japan, where numerous slow earthquakes have been detected (e.g., Obara, 2002; Ito et al., 2007; Nishimura et al., 2013).</p><p>Deep-focus earthquakes, frequently occurring in the Pacific slab below Southwestern Japan, can be applicable to the multi-band RF analysis because the local deep events and teleseismic events are similar in the slowness of the first-arrival phases. Local deep-focus events, however, have different variations in back azimuths from teleseismic events, which enables us to estimate seismological structures in a wider range of azimuths by stacking traces from both events. We carefully select the deep-focus events with longer S-P time than 40 sec and exclude triplication phases from mantle transition zones. Here we apply this method to short-period 3-component seismograms of Hi-net (NIED, Japan) in the Northeastern Kii Peninsula, where short-term slow slip events (SSEs) and episodic tremors are very active (e.g., Obara et al., 2010; Nishimura et al., 2013; Yabe & Ide, 2014).</p><p>Cross-sections of higher-frequency RFs (up to 2 Hz) show sharp and strong negative phases from the plate interface shallower than 35 km depth, which is one of the most active regions of episodic tremors (Obara et al., 2010). At the deeper portion, the higher-frequency RFs exhibit the mantle wedge structure with obscure phases of the plate interface, where minor and continuous tremor activities have been reported (Obara et al., 2010). These results suggest that episodic tremors accompanied by short-term SSEs occur on the interface between the continental crust and the oceanic crust, whereas the source regions of minor tremors are between the oceanic crust and the mantle wedge as indicated in Kato et al. (2010).</p>

scholarly journals Effect of normal stress on the frictional behavior of brucite: application to slow earthquakes at the subduction plate interface in the mantle wedge

Solid Earth ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 171-186
Author(s):  
Hanaya Okuda ◽  
Ikuo Katayama ◽  
Hiroshi Sakuma ◽  
Kenji Kawai
Keyword(s):  
Normal Stress ◽  
Small Volume ◽  
Mantle Wedge ◽  
Normal Stresses ◽  
Localized Deformation ◽  
Plate Interface ◽  
Frictional Behavior ◽  
Frictional Strength ◽  
Slow Earthquakes ◽  
Dry Conditions

Abstract. We report the results of friction experiments on brucite under both dry and wet conditions under various normal stresses (10–60 MPa). The final friction coefficients of brucite were determined to be 0.40 and 0.26 for the dry and wet cases, respectively, independent of the normal stress. Under dry conditions, velocity-weakening behavior was observed in all experiments at various normal stresses. Under wet conditions, velocity weakening was observed at low normal stress (10 and 20 MPa), whereas velocity strengthening was determined at a higher applied normal stress. Microstructural observations of recovered experimental samples indicate localized deformation within a narrow shear band, implying that a small volume of brucite can control the bulk frictional strength in an ultramafic setting. Among serpentinite-related minerals, weak and unstable frictional behavior of brucite under hydrated mantle wedge conditions may play a role in slow earthquakes at the subduction plate interface in the mantle wedge.

A Transmission Electron Microscopical Investigation of Phase Transformations in TiNi

1980 ◽  
Vol 38 ◽  
pp. 340-341
Author(s):  
P. Moine ◽  
G. M. Michal ◽  
R. Sinclair
Keyword(s):  
Electron Microscopy ◽  
Phase Transformations ◽  
Applied Stress ◽  
Structural Changes ◽  
Microscopical Investigation ◽  
Temperature Range ◽  
Transmission Electron ◽  
Electron Microscopical ◽  
Diffraction Effects ◽  
Microscopy Images

Premartensitic effects in near equiatomic TiNi have been pointed out by several authors(1-5). These include anomalous contrast in electron microscopy images (mottling, striations, etc. ),diffraction effects(diffuse streaks, extra reflections, etc.), a resistivity peak above Ms (temperature at which a perceptible amount of martensite is formed without applied stress). However the structural changes occuring in this temperature range are not well understood. The purpose of this study is to clarify these phenomena.

scholarly journals Hydrous oceanic crust hosts megathrust creep at low shear stresses

2020 ◽  
Vol 6 (22) ◽  
pp. eaba1529
Author(s):  
Christopher J. Tulley ◽  
Åke Fagereng ◽  
Kohtaro Ujiie
Keyword(s):  
Oceanic Crust ◽  
Shear Zones ◽  
Interface Strength ◽  
Shear Stresses ◽  
Plate Interface ◽  
Strength And Deformation ◽  
Transition Field ◽  
Flow Laws ◽  
Sw Japan ◽  
Low Shear

The rheology of the metamorphosed oceanic crust may be a critical control on megathrust strength and deformation style. However, little is known about the strength and deformation style of metamorphosed basalt. Exhumed megathrust shear zones exposed on Kyushu, SW Japan, contain hydrous metabasalts deformed at temperatures between ~300° and ~500°C, spanning the inferred temperature-controlled seismic-aseismic transition. Field and microstructural observations of these shear zones, combined with quartz grain-size piezometry, indicate that metabasalts creep at shear stresses <100 MPa at ~370°C and at shear stresses <30 MPa at ~500°C. These values are much lower than those suggested by viscous flow laws for basalt. The implication is that relatively weak, hydrous, metamorphosed oceanic crust can creep at low viscosities over a wide shear zone and have a critical influence on plate interface strength and deformation style around the seismic-aseismic transition.

scholarly journals Impact of interseismic deformation on phase transformations and rock properties in subduction zones

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Sebastian Cionoiu ◽  
Evangelos Moulas ◽  
Lucie Tajčmanová
Keyword(s):  
Phase Transformations ◽  
Subduction Zones ◽  
Systematic Investigation ◽  
Rock Properties ◽  
Principal Stresses ◽  
High Deformation ◽  
Alumina Inclusion ◽  
Rock Heterogeneity ◽  
Slow Earthquakes ◽  
The Impact

AbstractPhase transformations greatly affect physical properties of rocks and impose a first-order control on geodynamic processes. Under high deformation rates, rheological heterogeneities cause large spatial variations of stress in materials. Until now, the impact of higher deformation rates, rock heterogeneity and stress build up on phase transformations and material properties is not well understood. Here we show, that phase transitions are controlled by the stress build-up during fast deformation. In a deformation experiment (600 °C, 1.47 GPa), rock heterogeneity was simulated by a strong elliptical alumina inclusion in a weak calcite matrix. Under deformation rates comparable to slow earthquakes, calcite transformed locally to aragonite matching the distribution of maximum principal stresses and pressure (mean stress) from mechanical models. This first systematic investigation documents that phase transformations occur in a dynamic system during deformation. The ability of rocks to react during fast deformation rates may have serious consequences on rock rheology and thus provide unique information on the processes leading to giant ruptures in subduction zones.

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

Fluids in convergent margins: what do we know about their composition, origin, role in diagenesis and importance for oceanic chemical fluxes?

1991 ◽  
Vol 335 (1638) ◽  
pp. 243-259 ◽  
Keyword(s):  
Oceanic Crust ◽  
Volcanic Ash ◽  
Hydrate Formation ◽  
Convergent Margins ◽  
Pore Fluids ◽  
Hydrous Minerals ◽  
Porosity Reduction ◽  
Gas Hydrate Formation ◽  
The Difference ◽  
Internal Sources

The nature and origin of fluids in convergent margins can be inferred from geochemical and isotopic studies of the venting and pore fluids, and is attempted here for the Barbados Ridge, Nankai Trough and the convergent margin off Peru. Venting and pore fluids with lower than seawater Cl - concentrations characterize all these margins. Fluids have two types of source: internal and external. The three most important internal sources are: (1) porosity reduction; (2) diagenetic and metamorphic dehydration ; and (3) the breakdown of hydrous minerals. Gas hydrate formation and dissociation, authigenesis of hydrous minerals and the alteration of volcanic ash and/or the upper oceanic crust lead to a redistribution of the internal fluids and gases in vertical and lateral directions. The maximum amount of expelled water calculated can be ca. 7 m 3 a -1 m -1 , which is much less than the tens to more than 100 m 3 a -1 m -1 of fluid expulsion which has been observed. The difference between these figures must be attributed to external fluid sources, mainly by transport of meteoric water enhanced by mixing with seawater. The most important diagenetic reactions which modify the fluid compositions, and concurrently the physical and even the thermal properties of the solids through which they flow are: (1) carbonate recrystallization, and more importantly precipitation; (2) bacterial and thermal degradation of organic matter; (3) formation and dissociation of gas hydrates; (4) dehydration and transformation of hydrous minerals, especially of clay minerals and opal-A; and (5) alteration, principally zeolitization and clay mineral formation, of volcanic ash and the upper oceanic crust.

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