Complexity of Deep Low‐Frequency Earthquake Activity in Shikoku (Japan) Imaged From the Analysis of Continuous Seismic Data

Poiata, Natalia; Vilotte, J. P.; Shapiro, N. M.; Supino, Mariano; Obara, Kazushige

doi:10.1029/2021jb022138

Cited by 7 publications

(14 citation statements)

References 97 publications

(285 reference statements)

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“…Any accurate estimate of low-frequency earthquake fault slip must capture this episodic evolution that is characteristic of low-frequency seismicity (W. B. Frank et al, 2014;Shelly, 2017;Kato & Nakagawa, 2020;Poiata et al, 2021).…”

Section: Estimating the Seismic Fault Slip Of Low-frequency Earthquakesmentioning

confidence: 99%

“…Figure 2a shows the recurrence interval between consecutive events among these low‐frequency earthquake sources, with intermittent bursts of activity indicating concomitant slow slip (W. B. Frank et al., 2016). Any accurate estimate of low‐frequency earthquake fault slip must capture this episodic evolution that is characteristic of low‐frequency seismicity (W. B. Frank et al., 2014; Shelly, 2017; Kato & Nakagawa, 2020; Poiata et al., 2021).…”

Section: Connecting Geodetic and Seismic Estimates Of Fault Slipmentioning

confidence: 99%

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Subdaily Slow Fault Slip Dynamics Captured by Low‐Frequency Earthquakes

et al. 2023

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Geodetic positioning is the geophysical record of reference for slow slip events, but typical daily solutions limit studies of the evolution of slow slip to its long‐term dynamics. Accompanying seismic low‐frequency earthquakes located precisely in time and space provide an opportunity to image slow slip dynamics at subdaily time scales. Here we show that a high‐resolution time history of low‐frequency earthquake fault slip alone can reproduce the geodetic record of slow slip that we observe to be dominated by subdaily fault slip dynamics. However, a simple linear model cannot accommodate the complex dynamics present throughout the slow slip cycle, and an analysis of different phases of the slow slip cycle shows that the ratio of geodetic to seismic fault slip varies as a function of time. This suggests that the low‐frequency earthquake source region saturates as slow slip grows in moment and area. We propose that rheological heterogeneities at the plate boundary associated with low‐frequency earthquakes do not play a significant role in the slow slip rupture process, thus implying that their activity is incidental to the driving aseismic slip.

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Section: Estimating the Seismic Fault Slip Of Low-frequency Earthquakesmentioning

confidence: 99%

Section: Connecting Geodetic and Seismic Estimates Of Fault Slipmentioning

confidence: 99%

Subdaily Slow Fault Slip Dynamics Captured by Low‐Frequency Earthquakes

et al. 2023

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“…Inhomogeneity of the crust in the overlying plate is likely a result of orogeny, where crust thickening coincides with low Q p , low V p , and low V s . Such heterogeneity corresponds to a change in physical properties of the rocks in the vicinity of the subduction interface, which controls the rheology and hence tremor and SSE activity (Kita and Matsubara 2016;Nakajima and Hasegawa 2016;Poiata et al 2021).…”

Section: Conditions Within the Overriding Platementioning

confidence: 99%

Segmentation characteristics of deep, low-frequency tremors in Shikoku, Japan using machine learning approaches

Chen

Chiu

Obara

et al. 2023

Earth Planets Space

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Shikoku island, southwestern Japan lies in the western Nankai Trough and showcases along-strike segmentation of slow earthquake behavior. Whether the spatial variation of tremor behavior reflects the regional differences in structure/source properties and how much such differences can be recognized by the seismic signals themselves are two questions addressed in this paper. Taking advantage of advanced methods in recognizing and classifying signals using machine learning approaches, we attempt to answer them by conducting signal classification experiments in Shikoku. Based on the tremor catalog from 1 June 2014 to 31 March 2015, the tremors recorded in four different areas were treated as different classes and segmented into 60-s-long signals. The number of tremors in four different areas (A to D, from west to east) reached 15,000, 31,000, 10,000, and 16,000, respectively. To efficiently distinguish between tremors from different areas, we applied a k-nearest neighbor (k-NN) classifier with Fisher’s class separability criteria to select the optimal feature subset. The resulting classification performance reached more than 90% at all 12 stations. We further designed a triangle test to select the features that can better represent the differences in source properties between areas. We found that the most efficient features were associated with (1) the number of peaks in the temporal evolution of discrete Fourier transforms and (2) the energy distribution in the autocorrelation function (ACF). To match the difference in behavior revealed by the ACF, the size of the tremor zone, which mainly controls how long the seismic energy lasts in a tremor episode, was determined to be largest in Area B and smallest in Area C. The heterogeneity of the asperities in a tremor zone, which may control how spiky the tremor signals developed over time, was determined to be strong in Areas B and C. Together with previously documented variations in slow earthquake behavior in the same area, we finally propose a conceptual model that provides a better understanding of the regional differences in the tremor source properties in Shikoku, Japan. Graphical Abstract

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“…Single bursts of activity can be spaced by a few hours in the most active periods, which recur on the scale of months to years. This superimposition of timescales of recurrence—individual events, clusters, clusters of clusters, etc.—is characterized as a “scale‐free” phenomenon by studies on tremor (Idehara et al., 2014) and LFE activity (Frank et al., 2016; Poiata, Vilotte, Shapiro, Supino, & Obara, 2021). However, when looking at the largest bursts of activity in a given region, one or several characteristic timescales of recurrence can be estimated.…”

Section: Characterizing Tremor Intermittencementioning

confidence: 99%

Along‐Strike Segmentation of Seismic Tremor and Its Relationship With the Hydraulic Structure of the Subduction Fault Zone

Farge,

Jaupart,

Frank

et al. 2023

JGR Solid Earth

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Along the strike of subduction zones, tectonic tremor episodicity is segmented on a geologic scale. Here, we study how this segmentation reflects large‐scale variations of the structure and conditions of the fault interface where tremor is generated. We try to understand which properties of the hydraulic system of the fault allow elementary tremor sources to synchronize, leading to the emergence of long‐period, large‐scale episodic activity. We model tremor sources as being associated with rapid openings of low‐permeability valves in the fault zone, which channels the upward flow of metamorphic fluids. Valve openings cause pressure transients that allow interaction between sources. In such a system, tremor activity is thus controlled by unsteady fluid circulation. Using numerical simulations of fluid flow, we explore the impact of valve spatial distribution and fluid flux on the emergence of large‐scale patterns of tremor activity. We show that when valves are densely distributed and submitted to near‐critical input flux, they synchronize and generate more episodic activity. Based on our model, the most periodic and spatially coherent tremor bursts should thus be emitted from segments densely populated with valves, and therefore of lower permeability than less synchronized segments. The collective activity of their valve population is responsible for fluid‐pressure cycling at the subduction scale. In the tremor zone of Shikoku, Japan, the most temporally clustered segment coincides with a downgoing seamount chain, suggesting that the segmentation of the fault zone permeability, and hence of tremor activity, could be inherited from the topography of the subducting oceanic plate.

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Complexity of Deep Low‐Frequency Earthquake Activity in Shikoku (Japan) Imaged From the Analysis of Continuous Seismic Data

Cited by 7 publications

References 97 publications

Subdaily Slow Fault Slip Dynamics Captured by Low‐Frequency Earthquakes

Subdaily Slow Fault Slip Dynamics Captured by Low‐Frequency Earthquakes

Segmentation characteristics of deep, low-frequency tremors in Shikoku, Japan using machine learning approaches

Along‐Strike Segmentation of Seismic Tremor and Its Relationship With the Hydraulic Structure of the Subduction Fault Zone

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