Repeating deep tremors on the plate interface beneath Kyushu, southwest Japan

Yabe, Suguru; Ide, Satoshi

doi:10.5047/eps.2012.06.001

Cited by 16 publications

(13 citation statements)

References 21 publications

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“…Serpentinization of the mantle or hydration of the lower crust as a result from fluid fluxes from the megathrust would enhance seismic attenuation and anisotropy2526, explaining the high attenuation and large anisotropy observed above LFE-devoid areas. Therefore, the along-strike variations in seismic properties revealed in this study suggest that the overlying plate is less metamorphosed above areas with LFE activity and is significantly metamorphosed beneath Kanto, the Kii and Ise gaps and Kyushu, where no, or limited, tremor (that is, LFE) occurs at depths of 30–35 km (refs 1, 14). …”

Section: Discussionmentioning

confidence: 75%

“…In Nankai, there are two distinct spatial gaps in LFE and short-term SSE activity; a persistent gap of ∼60 km is observed in the Kii channel (the Kii gap) and a transient gap of ∼30 km occurs in the Ise bay (the Ise gap)1911. No, or limited, LFE (that is, tremor) activity occurs beneath Kanto and Kyushu11314 located at the margin-parallel extension of both sides of the well-defined zone of LFE activity. Therefore, an investigation of the seismic properties of different regions where LFEs are present or absent will yield a better understanding of factors controlling the genesis of LFEs.…”

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confidence: 99%

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Tremor activity inhibited by well-drained conditions above a megathrust

Nakajima

Hasegawa

2016

Nat Commun

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Tremor occurs on megathrusts under conditions of near-lithostatic pore-fluid pressures and extremely weakened shear strengths. Although metamorphic reactions in the slab liberate large amounts of fluids, the mechanism for enhancing pore-fluid pressures along the megathrust to near-lithostatic values remains poorly understood. Here we show anti-correlation between low-frequency earthquake (LFE) activity and properties that are markers of the degree of metamorphism above the megathrust, whereby LFEs occur beneath the unmetamorphosed overlying plate but are rare or limited below portions that are metamorphosed. The extent of metamorphism in the overlying plate is likely controlled by along-strike contrasts in permeability. Undrained conditions are required for pore-fluid pressures to be enhanced to near-lithostatic values and for shear strength to reduce sufficiently for LFE generation, whereas well-drained conditions reduce pore-fluid pressures at the megathrust and LFEs no longer occur at the somewhat strengthened megathrust. Our observations suggest that undrained conditions are a key factor for the genesis of LFEs.

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Section: Discussionmentioning

confidence: 75%

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confidence: 99%

Tremor activity inhibited by well-drained conditions above a megathrust

Nakajima

Hasegawa

2016

Nat Commun

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“…This coincidence is not surprising because the results of receiver function analysis are considered to be more accurate when estimating the location of a sharp structural change like the plate interface. Although the apparent vertical separation between tectonic tremor events (i.e., the plate interface) and intra-slab earthquakes seems to be slightly too large (approximately 15 km; Figure 4b) when compared with the typical separation of about 10 km in other subduction zones (Shelly et al 2006;Yabe and Ide 2013), the discrepancy might reflect the thick oceanic crust of the subducted Hikurangi Plateau. Therefore, we can conclude that tectonic tremor events do actually seem to occur around the plate interface in this region of the Hikurangi subduction zone.…”

Section: Relationship Between Tectonic Tremors and The Plate Interfacementioning

confidence: 77%

Along-strike variations in temperature and tectonic tremor activity along the Hikurangi subduction zone, New Zealand

2014

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In the Hikurangi subduction zone, situated along the east coast of the North Island, New Zealand, where the old oceanic Pacific Plate is subducting beneath the Australian Plate, several slow slip events and tectonic tremors have recently been documented. These observations are somewhat surprising because such slow seismic phenomena tend to be common in subduction zones where relatively young oceanic plate is subducting. The locations of tectonic tremors, down-dip limit of slow slip events and seismic coupling transition change along strike from greater depths in the south to shallower depths in the north, suggesting significant along-strike variations in the characteristics of the plate interface. Similar along-strike variations have been observed for other characteristic features of the Hikurangi subduction zone. Here, we demonstrate that along-strike variations observed for tectonic tremors, slow slip events, and seismic coupling can be explained by lateral differences in the thermal structure of the subduction zone, which are controlled mainly by variations in convergence rate and friction along the plate interface. To demonstrate this, we first confirm that tectonic tremors occur around the plate interface. Then, we calculate the thermal structure of the Hikurangi subduction zone using a two-dimensional finite difference code. To explain the along-strike variation in the heat flow observed in the forearc region, temperatures along the plate interface should be systematically higher in the northern region than in the southern region, which we interpret as a consequence of higher convergence rates and greater frictional heating in the northern region. We compare the along-strike variation of seismic characteristics with calculated thermal structure and highlight that this along-strike variation in temperature controls the depth of the brittle-ductile transition, which is consistent with the observed spatial variations in tectonic tremors, down-dip limit of slow slip events and seismic coupling. Our results suggest that tectonic tremors recorded within subduction zones reflect the transient rheology of the materials being subducted, which is controlled by variations in temperature along the plate interface.

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“…A clear exception is the subset for Kyushu, in which the tremor duration is anomalously short with respect to the recurrence interval. The tremors in Kyushu occurred in the region where the Kyushu-Palau ridge has supposedly subducted (Yabe and Ide 2013), perhaps resulting in a greater proportion of the accumulated stress being relieved aseismically by intertremor bursts whereas the frictional strength at the plate interface is locally high (Scholz and Small 1997).…”

Section: Regional and Global Variations In Temporal Clustering Propermentioning

confidence: 99%

Regional and global variations in the temporal clustering of tectonic tremor activity

2014

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The temporal distribution of tremor activity exhibits a highly non-Poissonian behavior, and its maximum period of non-Poissonian clustering statistically describes the recurrence interval of major tremor bursts. Here, we examine variations in the temporal clustering properties of tremor activity by assessing their characteristic times, which are determined by the maximum period of the non-Poissonian distribution. By applying a two-point correlation integral to some of the world's major tremor zones, including Shikoku, Kii-Tokai, and Kyushu in Japan; Cascadia, Jalisco, and Guerrero in Mexico; southern Chile; Taiwan; and Manawatu in New Zealand, we reveal local spatial variations in the temporal clustering properties in each tremor zone and show global-scale variations in tremor activity. The spatial variation in local tremor activity is characterized by a gradual transition in the along-dip direction and shorter-wavelength heterogeneities in the along-strike direction, possibly associated with a spatial change in frictional conditions at the plate interface and rheological conditions in the surrounding materials. The characteristic time correlates positively with locally measured median tremor duration, implying an inherent correlation between the moment release rate and the recurrence interval of tremors.

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Repeating deep tremors on the plate interface beneath Kyushu, southwest Japan

Cited by 16 publications

References 21 publications

Tremor activity inhibited by well-drained conditions above a megathrust

Tremor activity inhibited by well-drained conditions above a megathrust

Along-strike variations in temperature and tectonic tremor activity along the Hikurangi subduction zone, New Zealand

Regional and global variations in the temporal clustering of tectonic tremor activity

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