Seismic and geodetic evidence for the existence of hot materials beneath the Wakayama swarm activity, southwestern Japan

Yoshïda, Akio; Hosono, Kohji; Takayama, Hiromi; Kobayashi, Akio; Maeda, Kenji

doi:10.1016/j.tecto.2011.06.023

Cited by 13 publications

(14 citation statements)

References 34 publications

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“…Combined with these observations, the long-term persistence of the dome-like pattern of seismicity (Yoshida et al 2011; Japan Meteorological Agency 2014) and the pressurized source producing uplift and dilatation at the surface (Figure 1) indicate that fluids such as water or partial melt beneath the seismic swarm area are key factors driving the seismic swarm activity ( Figure 5). …”

Section: Resultsmentioning

confidence: 91%

“…One of the most intensive non-volcanic seismic swarms in Japan is located in the Wakayama district of southwest Japan, far from the present volcanic front (e.g., Mizoue et al 1983;Kato et al 2010a;Yoshida et al 2011) (Figure 1). Here, the Philippine Sea slab is subducting from a southeast-south direction beneath the Kii Peninsula.…”

Section: Introductionmentioning

confidence: 99%

“…In addition, the Wakayama district has unique geophysical characteristics such as high heat flow (Tanaka et al 2004), uplift movement on the surface that implies a pressurized source (Yoshida et al 2011), and deep lowfrequency earthquakes (LFEs) around the island arc Moho. Kato et al (2010a) proposed that diorite has intruded into the bottom of the seismic swarm area and that fluids released from the solidifying diorite are invading the rocks immediately above, based on a local seismic tomographic image of the southern edge of the seismic swarm area.…”

Section: Introductionmentioning

confidence: 99%

“…Gray circles denote all of the earthquakes identified by JMA during the seismic observing period. Solid contours represent annual rate of uplift ≥4 mm/year (with an interval of 1 mm/year) observed by geodetic measurements (Yoshida et al 2011). Major active faults are drawn as red lines.…”

Section: Introductionmentioning

confidence: 99%

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Non-volcanic seismic swarm and fluid transportation driven by subduction of the Philippine Sea slab beneath the Kii Peninsula, Japan

et al. 2014

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To understand the mechanism of an intensive non-volcanic seismic swarm in the Kii Peninsula, Japan, we used a dense seismic linear array to measure fine-scale variations of seismic velocities and converted teleseismic waves. A low-velocity anomaly confined to just beneath the seismic swarm area is clearly imaged, which correlates spatially with an uplifted surface area and a highly conductive and strong attenuative body. These results suggest that fluids such as partial melt or water are present beneath this non-volcanic seismic swarm area. It is notable that the island arc Moho below the seismic swarm area is at a depth of approximately 32 km in the northern part of the seismic swarm area and shallows to approximately 20 km towards the south, due to the raised structure of the serpentinized mantle wedge. In addition, we show that the hydrated oceanic crust of the subducting Philippine Sea slab is characterized by low velocities with a high Poisson's ratio at depths of less than 40 km. In contrast, dehydration conversion from oceanic basalt to eclogite takes place at depths greater than 50 km. Water released from the subducting oceanic crust could cause serpentinization of the mantle wedge and infiltration into the forearc base of the overlying plate. The interaction between dehydration of the subducting oceanic crust and hydration of the mantle wedge and overlying plate exerts an important role in driving the non-volcanic seismic swarm activity in the Kii Peninsula.

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Section: Resultsmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Non-volcanic seismic swarm and fluid transportation driven by subduction of the Philippine Sea slab beneath the Kii Peninsula, Japan

et al. 2014

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“…In the Wakayama region, heat flow data and seismic velocity structure indicate the presence of hot fluid beneath the hypocenters (e.g., Kato et al 2010Kato et al , 2014Matsumoto 2007;Omuralieva et al 2012;Tanaka et al 2004;Yoshida et al 2011). Nakajima and Hasegawa (2007) pointed out that high seismicity in this study area is probably related to locally concentrated fluids.…”

Section: Discussionmentioning

confidence: 99%

Complex microseismic activity and depth-dependent stress field changes in Wakayama, southwestern Japan

Maeda

Matsuzawa

Toda

et al. 2018

Earth Planets Space

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We examined the spatial relationship between seismicity and upper crustal structure in the Wakayama region, northwestern Kii Peninsula, Japan, by investigating microearthquake focal mechanisms and the local stress field. The focal mechanisms of most events studied fall into three categories: (1) normal faulting with N-S-oriented T-axes mainly occurring at shallow depths, (2) reverse faulting with E-W-oriented P-axes dominating at intermediate depths, and (3) strike-slip faulting with N-S-oriented T-axes and E-W-oriented P-axes mainly seen at greater depths. The stress field varies with depth: the shallow part is characterized by a strike-slip-type stress regime with N-S tension and E-W compression, while the deep part is characterized by an E-W compressional stress regime consistent with reverse faulting. The depth-dependent stress regime can be explained by thermal stress caused by a heat source, as expected from geophysical observations. Geologic faults, acting as weak planes, might contribute to generate shallow normal fault-type and deeper strike-slip fault-type microearthquakes.

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Temperature control on deep tectonic tremor belt in the Nankai subduction zone

Ikuta

Kobayashi

Arai

et al. 2022

Preprint

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Deep tectonic tremors occur in the Nankai subduction zone, defining a belt-like zone with a width of a few ten km located at depths between 30 and 55 km along upper surface of the subducting Philippine sea slab. We interpret the geometry of the tremor belt based on temperature calculations. Time evolution of temperature is calculated using a 3-D heat conduction assuming constant geometry of the slab and the present-day plate convergence velocity. The results show that the tremors occur along the 450°C isotherm along the slab surface where the mantle wedge can be non-convective and already well-serpentinized. Two gaps of the tremor belts are explained by different mechanisms. The Ise gap is where the hanging wall is not mantle wedge but crust. The Kii Gap is not a gap orthogonal to the plate convergence direction, but only appears to be a gap because the isotherm of the plate surface steps in the plate convergence direction. The tremors can be caused by high pore-fluid pressure conditions due to aqueous fluids released by dehydration reactions in blueschist-facies oceanic crust to form eclogite facies. The depth of the tremor belt corresponds to that of decoupled, non-convective mantle wedge. Since the temperature and pressure are within the serpentinite stable condition, the released fluid would normally be absorbed by serpentinization of the mantle wedge peridotite. However, since the non-convective mantle wedge is already well serpentinized from exposure to previously released fluids, the newly released fluid is not absorbed and increases the pore pressure. Hosted file essoar.10512557.1.docx available at https://authorea.com/users/549855/articles/603763temperature-control-on-deep-tectonic-tremor-belt-in-the-nankai-subduction-zone Hosted file suppinfo.docx available at https://authorea.com/users/549855/articles/603763-temperaturecontrol-on-deep-tectonic-tremor-belt-in-the-nankai-subduction-zone Temperature control on deep tectonic tremor belt in the Nankai subduction zone

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Seismic and geodetic evidence for the existence of hot materials beneath the Wakayama swarm activity, southwestern Japan

Cited by 13 publications

References 34 publications

Non-volcanic seismic swarm and fluid transportation driven by subduction of the Philippine Sea slab beneath the Kii Peninsula, Japan

Non-volcanic seismic swarm and fluid transportation driven by subduction of the Philippine Sea slab beneath the Kii Peninsula, Japan

Complex microseismic activity and depth-dependent stress field changes in Wakayama, southwestern Japan

Temperature control on deep tectonic tremor belt in the Nankai subduction zone

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