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>

The 2016 Mw 7.8 Kaikoura earthquake and its relationship to tremors.

2020 ◽  
Author(s):  
Pierre Romanet ◽  
Florent Aden-Antoniow ◽  
Satoshi Ide
Keyword(s):  
Cross Correlation ◽  
Seismic Energy ◽  
Slow Slip ◽  
Unexpected Events ◽  
Slow Slip Event ◽  
Slow Earthquakes ◽  
Slip Event ◽  
Kaikoura Earthquake ◽  
The Relationship

<p>The relationship between slow earthquake and regular earthquake is fundamental question in seismology. It was already shown that some slow slip event may have led to some megathrust event. In return, passing surface wave from earthquake may also trigger tremors and slow slip event. Documenting these possible triggering effects between slow and fast events is of primary importance to understand them.</p><p>In this study we will focus more particularly on Marlborough region, in a region that was subject to the Mw 7.8 2016 Kaikoura earthquake. Two years before Kaikoura earthquake, we observed a Northeast to Southwest migration of tremors, getting closer to the hypocenter of Kaikoura earthquake. Despite being speculative, this may indicate that a slow slip event is happening shortly before Kaikoura earthquake, which is also supported by a small signal in two GPS stations nearby. After the earthquake, the rate of tremors increased in the region. Studying the relationship between tremors and the Kaikoura earthquake may provide some information on the role of the subduction in the region, as well as provide a new documented interaction of slow earthquakes with a crustal earthquake.</p><p>To detect and locate tremors, we use broadband and shortband velocity traces from the GeoNet network. The traces are bandpass filtered between 2-8Hz, and transform into envelope. Then we apply a classic cross-correlation technic to detect and locate the events. To remove unexpected events (i.e.: earthquakes), we used a criteria base on seismic energy and duration. Finally, we manually check each velocity traces and spectrograms.</p>

Slow Earthquakes Linked Along Dip in the Nankai Subduction Zone: Fig. 1

Science ◽  
2010 ◽  
Vol 330 (6010) ◽  
pp. 1502-1502 ◽  
Author(s):  
Hitoshi Hirose ◽  
Youichi Asano ◽  
Kazushige Obara ◽  
Takeshi Kimura ◽  
Takanori Matsuzawa ◽  
...  
Keyword(s):  
Low Frequency ◽  
Temporal Correlation ◽  
Rupture Zone ◽  
Slow Slip ◽  
Southwest Japan ◽  
Slow Earthquakes ◽  
Slip Event ◽  
Nankai Subduction Zone ◽  
Stress Buildup

We identified a strong temporal correlation between three distinct types of slow earthquakes distributed over 100 kilometers along the dip of the subducting oceanic plate at the western margin of the Nankai megathrust rupture zone, southwest Japan. In 2003 and 2010, shallow very-low-frequency earthquakes near the Nankai trough as well as nonvolcanic tremor at depths of 30 to 40 kilometers were triggered by the acceleration of a long-term slow slip event in between. This correlation suggests that the slow slip might extend along-dip between the source areas of deeper and shallower slow earthquakes and thus could modulate the stress buildup on the adjacent megathrust rupture zone.

scholarly journals Shallow slow slip events along the Nankai Trough detected by GNSS-A

2020 ◽  
Vol 6 (3) ◽  
pp. eaay5786 ◽  
Author(s):  
Yusuke Yokota ◽  
Tadashi Ishikawa
Keyword(s):  
Subduction Zones ◽  
Nankai Trough ◽  
Plate Boundary ◽  
Low Frequency ◽  
Satellite System ◽  
Boundary Region ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Combination Technique ◽  
Slow Earthquakes

Various slow earthquakes (SEQs), including tremors, very low frequency events, and slow slip events (SSEs), occur along megathrust zones. In a shallow plate boundary region, although many SEQs have been observed along pan-Pacific subduction zones, SSEs with a duration on the order of a year or with a large slip have not yet been detected due to difficulty in offshore observation. We try to statistically detect transient seafloor crustal deformations from seafloor geodetic data obtained by the Global Navigation Satellite System-Acoustic (GNSS-A) combination technique, which enables monitoring the seafloor absolute position. Here, we report the first detection of signals probably caused by shallow large SSEs along the Nankai Trough and indicate the timings and approximate locations of probable SSEs. The results show the existence of large SSEs around the shallow side of strong coupling regions and indicate the spatiotemporal relationship with other SEQ activities expected in past studies.

scholarly journals Slow Slip Events Following the 2002 Mw 7.1 Hualien Offshore Earthquake Afterslip

2021 ◽  
Author(s):  
Sean Kuanhsiang Chen ◽  
Yih-Min Wu ◽  
Yu-Chang Chan
Keyword(s):  
Coulomb Stress ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Slow Slip Event ◽  
Coulomb Stress Changes ◽  
Stress Changes ◽  
Slip Event ◽  
Slip Region ◽  
Recurrence Intervals ◽  
Offshore Earthquake

Abstract The recurrence intervals of slow slip events may increase gradually after a large earthquake during the afterslip. Stress perturbations during coseismic and postseismic periods may result in such an increase of intervals. However, the increasing recurrence intervals of slow slip events are rarely observed during an afterslip. The evolution process along with the afterslip remains unclear. We report an observation of slow slip events following the 2002 Mw 7.1 Hualien offshore earthquake afterslip in the southernmost Ryukyu subduction zone. Slow slip events in 2005, 2009, and 2015 are adjacent to the Mw 7.1 earthquake hypocenter. An increasing slow-slip interval of 3.1, 4.2, and 6.2 years has been observed after the earthquake. We calculated coseismic and postseismic slips from the Mw 7.1 earthquake and then estimated the Coulomb stress changes in the slow slip region. The Mw 7.1 earthquake has contributed positive Coulomb stresses to both the 2005 slow-slip region and 2009/2015 repeating slow-slip region. The coseismic and postseismic Coulomb stress change on the 2005 slow-slip region is approximately 0.05 MPa and 0.035 MPa, respectively. However, both Coulomb stress changes on the 2009/2015 repeating slow-slip region are not over 0.03 MPa. The ongoing afterslip following the Mw 7.1 earthquake last for at least five years, evolving with a decaying stress rate with time. The long-term stress perturbations may be able to trigger the 2005 slow slip event during the afterslip. The 2009 slow slip event seems to be influenced by the afterslip as well. Postseismic stress evolution and frictional and stressed conditions of the slow-slip region can be a reason to affect the evolution process of slow slip events intervals.

scholarly journals Slip bursts during coalescence of slow slip events in Cascadia

2021 ◽  
Author(s):  
Quentin Bletery ◽  
Jean-Mathieu Nocquet
Keyword(s):  
Laboratory Experiments ◽  
Experimental Studies ◽  
Slow Slip ◽  
Ground Displacement ◽  
Gps Measurements ◽  
Dynamic Simulations ◽  
Slow Slip Events ◽  
Slow Slip Event ◽  
Slip Event ◽  
Continuous Gps

<p>Both laboratory experiments and dynamic simulations suggest that earthquakes can be preceded by a precursory phase of slow slip. Observing processes leading to an acceleration or spreading of slow slip along faults is therefore key to understand the dynamics potentially leading to seismic ruptures. Here, we use continuous GPS measurements of the ground displacement to image the daily slip along the fault beneath Vancouver Island during a slow slip event in 2013. We image the coalescence of three originally distinct slow slip fronts merging together. We show that during coalescence phases lasting for 2 to 5 days, the rate of energy (moment) release significantly increases. This observation supports the view proposed by theoretical and experimental studies that the coalescence of slow slip fronts is a possible mechanism for initiating earthquakes.</p>

scholarly journals Stress state along the western Nankai Trough subduction zone inferred from b-values, long-term slow-slip events, and low-frequency earthquakes

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Keita Chiba
Keyword(s):  
Low Frequency ◽  
Value Distribution ◽  
Focal Region ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Megathrust Earthquakes ◽  
Source Regions ◽  
Slow Earthquakes ◽  
Subducting Plate

AbstractThe b-value of the Gutenberg–Richter law represents the ratio of earthquake magnitude to frequency of occurrence and is inversely proportional to differential stress. Repeating long-term slow-slip events (SSEs) and low-frequency earthquakes (LFEs) occur at subducting plate interfaces and have stress-dependent characteristics near the interface. In this study, a comprehensive regional b-value distribution is produced for the western Nankai Trough region, which highlights the relationship between b-values, SSEs, and LFEs. b-values vary along the strike direction of the subducting plate and are significantly lower $$ \left( {b \sim 0.6} \right) $$b∼0.6 in central Shikoku district than elsewhere, where LFEs frequently occur. However, b-values in the source regions of other LFEs are moderate to high. These findings imply that b-values in the focal region are controlled by more than the LFE source process; indeed, if this source process were solely responsible, then high b-values would be expected. Meanwhile, the $$ V_{P} /V_{S} $$VP/VS and QP around the plate interface in central Shikoku estimated from seismic velocity and attenuation structure are smaller and larger than those in other regions with LFEs, respectively. SSEs with the migration toward central Shikoku also occurred during the analysis period, suggesting significant accumulation of shear stresses in the focal region, which reduced the b-values. These findings suggest that the spatial distributions of b-values are influenced by complicated stress and shear strength perturbations caused by SSEs and LFEs. On the other hand, the b-values in the region that underwent the greatest slip during the 1946 Nankai earthquake are not necessarily low, although the area covered by the b-value distribution is small owing to the lack of events on the updip side. Whereas the asperity areas of huge earthquakes are characterized by low b-values, the b-value distribution in the Nankai megathrust area is more complicated. It is considered that slow earthquakes, including SSEs and LFEs, are related to megathrust earthquakes via stress transfer from slow earthquakes to adjacent megathrust source regions. A unified analysis of b-values in the source regions of slow and megathrust earthquakes may be required to make precise estimates of the seismic hazard produced by a megathrust event.

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