scholarly journals Activation of very low frequency earthquakes by slow slip events in the Ryukyu Trench

2015 ◽  
Vol 42 (4) ◽  
pp. 1076-1082 ◽  
Author(s):  
Mamoru Nakamura ◽  
Naoya Sunagawa
Keyword(s):  
Low Frequency ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Ryukyu Trench ◽  
Very Low Frequency

scholarly journals Shallow very-low-frequency earthquakes accompany slow slip events in the Nankai subduction zone

2018 ◽  
Vol 9 (1) ◽  
Author(s):  
Masaru Nakano ◽  
Takane Hori ◽  
Eiichiro Araki ◽  
Shuichi Kodaira ◽  
Satoshi Ide
Keyword(s):  
Subduction Zone ◽  
Low Frequency ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Very Low Frequency ◽  
Nankai Subduction Zone

Possible shallow slow slip events in Hyuga-nada, Nankai subduction zone, inferred from migration of very low frequency earthquakes

2015 ◽  
Vol 42 (2) ◽  
pp. 331-338 ◽  
Author(s):  
Youichi Asano ◽  
Kazushige Obara ◽  
Takanori Matsuzawa ◽  
Hitoshi Hirose ◽  
Yoshihiro Ito
Keyword(s):  
Subduction Zone ◽  
Low Frequency ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Very Low Frequency ◽  
Nankai Subduction Zone

Observing seismic signatures of slow slip events with unsupervised learning

2021 ◽  
Author(s):  
Leonard Seydoux ◽  
Michel Campillo ◽  
René Steinmann ◽  
Randall Balestriero ◽  
Maarten de Hoop
Keyword(s):  
Clustering Algorithm ◽  
Low Frequency ◽  
Seismic Signal ◽  
Geodetic Data ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Slow Slip Event ◽  
Intermittent Behavior ◽  
Slow Earthquakes ◽  
Slip Event

<p>Slow slip events are observed in geodetic data, and are occasionally associated with seismic signatures such as slow earthquakes (low-frequency earthquakes, tectonic tremors). In particular, it was shown that swarms of slow earthquake can correlate with slow slip events occurrence, and allowed to reveal the intermittent behavior of several slow slip events. This observation was possible thanks to detailed analysis of slow earthquakes catalogs and continuous geodetic data, but in every case, was limited to particular classes of seismic signatures. In the present study, we propose to infer the classes of seismic signals that best correlate with the observed geodetic data, including the slow slip event. We use a scattering network (a neural network with wavelet filters) in order to find meaningful signal features, and apply a hierarchical clustering algorithm in order to infer classes of seismic signal. We then apply a regression algorithm in order to predict the geodetic data, including slow slip events, from the occurrence of inferred seismic classes. This allow to (1) identify seismic signatures associated with the slow slip events as well as (2) infer the the contribution of each classes to the overall displacement observed in the geodetic data. We illustrate our strategy by revisiting the slow-slip event of 2006 that occurred beneath Guerrero, Mexico.</p>

scholarly journals Using low-frequency earthquakes to monitor slow tectonic deformation in the central Southern Alps, New Zealand

2021 ◽  
Author(s):  
◽  
Laura-May Baratin Wachten
Keyword(s):  
New Zealand ◽  
Matched Filter ◽  
Low Frequency ◽  
Southern Alps ◽  
Focal Mechanisms ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Event Time ◽  
Alpine Fault ◽  
Occurrence Patterns

<p>This thesis involves the study of low-frequency earthquakes (LFEs) in the central Southern Alps. The Alpine Fault is the principal locus of deformation within the Australia–Pacific plate boundary in the South Island of New Zealand and it is late in its typical ∼300-year seismic cycle. Surveying the seismicity associated with slow deformation in the vicinity of the Alpine Fault may provide constraints on the stresses acting on a major transpressive margin prior to an anticipated great (≥M8) earthquake. Here, we use 8 years of data from the Southern Alps Microearthquake Borehole Array (SAMBA) (amongst those, 3 years of data were collected as part of this project) in order to: (1) generate an updated LFE catalogue using an improved matched-filter technique that incorporates phase-weighted stacking; (2) compute LFE focal mechanisms and invert them to infer the crustal stress field on the deep extent of the Alpine Fault; (3) expand the LFE catalogue to cover a wider range of spatial/temporal behaviours; (4) study LFE families’ characteristics to identify periods where slow slip might happen.  We first use fourteen primary LFE templates in an iterative matched-filter and stacking routine, which allows the detection of similar signals and produces LFE families sharing common locations. We generate an 8-yr catalogue containing 10,000 LFEs that are combined for each of the 14 LFE families using phase-weighted stacking to produce signals with the highest possible signal-to-noise ratios. We find LFEs to occur almost continuously during the 8-yr study period and we highlight two types of LFE distributions: (1) discrete behaviour with an inter-event time exceeding 2 minutes; (2) burst-like behaviour with an inter-event time below 2 minutes. The discrete events are interpreted as small-scale frequent deformation on the deep extent of the Alpine Fault and the LFE bursts (corresponding in most cases to known episodes of tremor or large regional earthquakes) are interpreted as brief periods of increased slip activity indicative of slow slip. We compute improved non-linear earthquake locations using a 3D velocity model and find LFEs to occur below the seismogenic zone at depths of 17–42 km, on or near the hypothesised deep extent of the Alpine Fault. We then compute the first estimates of LFE focal mechanisms associated with continental faulting. Focal mechanisms, in conjunction with recurrence intervals, are consistent with quasi-continuous shear faulting on the deep extent of the Alpine Fault.  We then generate a new catalogue that regroups hundreds of LFE families. This time 638 synthetic LFE waveforms are generated using a 3D grid and used as primary templates in a matched-filter routine. Of those, 529 templates yield enough detections during the first iteration of the matched-filter routine (≥ 500 detections over the 8-yr study period) and are kept for further analysis. We then use the best 25% of correlated events for each LFE family to generate linear stacks which create new LFE templates. From there, we run a second and final iteration of the matched-filter routine with the new LFE templates to obtain our final LFE catalogue. The remaining 529 templates detect between 150 and 1,671 events each totalling 300,996 detections over the 8-yr study period. Of those 529 LFEs, we manage to locate 378 families. Their depths range between 11 and 60 km and LFEs locate mainly in the southern part of the SAMBA network. We finally examine individual LFE family rates and occurrence patterns. They indicate that LFE sources seem to evolve from an episodic or ‘stepped’ to a continuous behaviour with depth. This transition may correspond to an evolution from a stick-slip to a stable-sliding slip regime. Hence, we propose that the distinctive features of LFE occurrence patterns reflect variations in the in-situ stress and frictional conditions at the individual LFE source locations on the Alpine Fault.  Finally, we use this new extensive catalogue as a tool for in-depth analyses of the deep central Alpine Fault structure and its slip behaviour. We identify eight episodes of increased LFE activity between 2009 and 2017 and provide time windows for further investigations of tremor and slow slip. We also study the spatial and temporal behaviours of LFEs and find that LFEs with synchronous occurrence patterns tend to be clustered in space. We thus suggest that individual LFE sources form spatially coherent clusters that may represent localised asperities or elastic patches on the deep Alpine Fault interface. We infer that those clusters may have a similar rheological response to tectonic forcing or to potential slow slip events. Eventually, we discover slow (10km/day) and rapid (∼20-25km/h) migrations of LFEs along the Alpine Fault. The slow migration might be controlled by slow slip events themselves while the rapid velocities could be explained by the LFE sources’ intrinsic properties.</p>

scholarly journals Detection of Deep Low-frequency Earthquakes in the Nankai Subduction Zoneover 11 Years Usingamatched Filter Technique

2020 ◽  
Author(s):  
Aitaro Kato ◽  
Shigeki Nakagawa
Keyword(s):  
Matched Filter ◽  
Low Frequency ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Filter Technique ◽  
Strike Direction ◽  
Episodic Tremor And Slip ◽  
Spatio Temporal ◽  
Episodic Tremor

Abstract To improve our understanding of the long-term behavior of low-frequency earthquakes (LFEs) along the tremor belt of the Nankai subduction zone, we applied a matched filter technique to continuous seismic data recorded by a dense and highly sensitive seismic network over an 11year window, April 2004 to August 2015. We detected a total of ~510,000 LFEs, or ~23× the number of LFEs in the JMA catalog for the same period. During long-term slow slip events (SSEs) in the Bungo Channel, a series of migrating LFEbursts intermittently occurred along the fault-strike direction, with slow hypocenter propagation. Elastic energy released by long-term SSEs appears to control the extent of LFE activity. We identify slowlymigrating fronts of LFEs during major episodic tremor and slip (ETS)events, which extend over distances of up to 100 km and follow diffusion-like patterns of spatial evolution with a diffusion coefficient of ~104 m2/s. This migration pattern closely matches the spatio-temporal evolution of tectonictremors reported by previous studies. At shorter distances, up to 15 km, we discovered rapid diffusion-like migrationof LFEs with a coefficient of ~105 m2/s. We also recognize that rapid migration of LFEs occurred intermittently in many streaks during major ETS episodes. These observations suggest that slow slip transients contain a multitude of smaller, temporally clustered fault slip events whose evolution is controlled by a diffusional process.

scholarly journals Daily measurement of slow slip from low-frequency earthquakes is consistent with ordinary earthquake scaling

2019 ◽  
Vol 5 (10) ◽  
pp. eaaw9386 ◽  
Author(s):  
William B. Frank ◽  
Emily E. Brodsky
Keyword(s):  
Full Range ◽  
Low Frequency ◽  
Blind Spot ◽  
Earthquake Activity ◽  
Slow Slip ◽  
Earthquake Cycle ◽  
Slow Slip Events ◽  
Event Time ◽  
Earthquake Scaling ◽  
The Moment

Slow slip transients on faults can last from seconds to months and stitch together the earthquake cycle. However, no single geophysical instrument is able to observe the full range of slow slip because of bandwidth limitations. Here, we connect seismic and geodetic data from the Mexican subduction zone to explore an instrumental blind spot. We establish a calibration of the daily median amplitude of the seismically recorded low-frequency earthquakes to the daily geodetically recorded moment rate of previously established slow slip events. This calibration allows us to use the precise evolution of low-frequency earthquake activity to quantitatively measure the moment of smaller, subdaily slip events that are unresolvable by geodesy alone. The resulting inferred slow slip moments scale with duration and inter-event time like ordinary earthquakes. These new quantifications help connect slow and fast events in a broad spectrum of transient slip and suggest that slow slip events behave much like ordinary earthquakes.

scholarly journals Detection of deep low-frequency earthquakes in the Nankai subduction zone over 11 years using a matched filter technique

2020 ◽  
Author(s):  
Aitaro Kato ◽  
Shigeki Nakagawa
Keyword(s):  
Subduction Zone ◽  
Matched Filter ◽  
Low Frequency ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Filter Technique ◽  
Episodic Tremor And Slip ◽  
Nankai Subduction Zone ◽  
Spatio Temporal

Abstract To improve our understanding of the long-term behavior of low-frequency earthquakes (LFEs) along the tremor belt of the Nankai subduction zone, we applied a matched filter technique to continuous seismic data recorded by a dense and highly sensitive seismic network over an 11 year window, April 2004 to August 2015. We detected a total of ~510,000 LFEs, or ~23× the number of LFEs in the JMA catalog for the same period. During long-term slow slip events (SSEs) in the Bungo Channel, a series of migrating LFE bursts intermittently occurred along the fault-strike direction, with slow hypocenter propagation. Elastic energy released by long-term SSEs appears to control the extent of LFE activity. We identify slowly migrating fronts of LFEs during major episodic tremor and slip (ETS) events, which extend over distances of up to 100 km and follow diffusion-like patterns of spatial evolution with a diffusion coefficient of ~10 4 m 2 /s. This migration pattern closely matches the spatio-temporal evolution of tectonic tremors reported by previous studies. At shorter distances, up to 15 km, we discovered rapid diffusion-like migration of LFEs with a coefficient of ~10 5 m 2 /s. We also recognize that rapid migration of LFEs occurred intermittently in many streaks during major ETS episodes. These observations suggest that slow slip transients contain a multitude of smaller, temporally clustered fault slip events whose evolution is controlled by a diffusional process.

Detecting tectonic tremor during slow slip events in Costa-Rica using templates of ordinary earthquakes

2021 ◽  
Author(s):  
Julien Renou ◽  
Jessica Hawthorne
Keyword(s):  
Costa Rica ◽  
Matched Filter ◽  
Low Frequency ◽  
Seismic Energy ◽  
Velocity Model ◽  
Field Method ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Small Areas ◽  
Local Earthquakes

&lt;p&gt;Slow slip events (SSEs) have been observed beneath the Nicoya peninsula in Costa-Rica for more than 10 years, and are accompanied by tremor activity both updip and downdip of the seismogenic region. However, tremor detection in this region can be challenging and time-consuming, as many local earthquakes occur amidst the tremor, so envelope-based techniques do not perform as well as they do in other regions. Matched-filter techniques are more appropriate to detect many of the individual low-frequency earthquakes (LFEs) that constitute tremor, but these techniques can also be time-consuming and restricted to small areas because they require a set of template seismograms for each LFE family.&lt;/p&gt;&lt;p&gt;In this study, we attempt to take advantage of the many local earthquakes to use the ordinary earthquakes' waveforms as templates to detect tremor all along the subduction interface. We use an extension of matched-filter techniques, a phase coherence (or matched field) method which can identify signals from locations near the template event even if the template and target signals have different source time functions. Because of this specificity of the coherence method, we should be able to detect tremor co-located with an ordinary earthquake, as long as they share similar Green's functions.&lt;/p&gt;&lt;p&gt;We create template waveforms from a catalog created by the Nicoya Seismic Cycle Observatory, whose events are located using local 3-D velocity model (DeShon et al. 2006). We first apply the method during a SSE event in June 2009, and initial investigations suggest that the tremor and earthquakes are similar enough: high coherence values are found at time of known tremor. Bursts of activity with various duration close to the trench are successfully detected, and their location is consistent with slip distribution of the SSE. Our final goal is to identify potential migration of these bursts related to the propagation of the main front of the SSE, as well as investigate the relation between their released seismic energy and duration. These findings will be finally discussed in comparison with tremor characteristics in other subduction areas.&lt;/p&gt;

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