scholarly journals Automatic Detection of Slow Slip Events Using the PICCA: Application to Chilean GNSS Data

2021 ◽  
Vol 9 ◽  
Author(s):  
F. Donoso ◽  
M. Moreno ◽  
F. Ortega-Culaciati ◽  
J. R. Bedford ◽  
R. Benavente
Keyword(s):  
Time Series ◽  
Subduction Zones ◽  
Onset Time ◽  
Transient Signal ◽  
Slow Slip ◽  
Independent Components ◽  
Slow Earthquakes ◽  
Transient Events ◽  
Spatial Detection

The detection of transient events related to slow earthquakes in GNSS positional time series is key to understanding seismogenic processes in subduction zones. Here, we present a novel Principal and Independent Components Correlation Analysis (PICCA) method that allows for the temporal and spatial detection of transient signals. The PICCA is based on an optimal combination of the principal (PCA) and independent component analysis (ICA) of positional time series of a GNSS network. We assume that the transient signal is mostly contained in one of the principal or independent components. To detect the transient, we applied a method where correlations between sliding windows of each PCA/ICA component and each time series are calculated, obtaining the stations affected by the slow slip event and the onset time from the resulting correlation peaks. We first tested and calibrated the method using synthetic signals from slow earthquakes of different magnitudes and durations and modelled their effect in the network of GNSS stations in Chile. Then, we analyzed three transient events related to slow earthquakes recorded in Chile, in the areas of Iquique, Copiapó, and Valparaíso. For synthetic data, a 150 days event was detected using the PCA-based method, while a 3 days event was detected using the ICA-based method. For the real data, a long-term transient was detected by PCA, while a 16 days transient was detected by ICA. It is concluded that simultaneous use of both signal separation methods (PICCA) is more effective when searching for transient events. The PCA method is more useful for long-term events, while the ICA method is better suited to recognize events of short duration. PICCA is a promising tool to detect transients of different characteristics in GNSS time series, which will be used in a next stage to generate a catalog of SSEs in Chile.

scholarly journals An intraplate slow earthquake observed by a dense GPS network in Hokkaido, northernmost Japan

2014 ◽  
Vol 200 (1) ◽  
pp. 144-148 ◽  
Author(s):  
Mako Ohzono ◽  
Hiroaki Takahashi ◽  
Masayoshi Ichiyanagi
Keyword(s):  
Subduction Zones ◽  
Earthquake Swarm ◽  
Tectonic Activity ◽  
Maximum Magnitude ◽  
Slow Slip ◽  
Localized Deformation ◽  
Slow Earthquake ◽  
Magnitude Scaling ◽  
Duration Magnitude ◽  
Slow Earthquakes

Abstract An intraplate slow earthquake was detected in northernmost Hokkaido, Japan, by a dense network of the global navigation satellite system. Transient abnormal acceleration of <12 mm was observed during the period 2012 July to 2013 January (∼5.5 months) at several sites. The spatial displacement distribution suggests that a localized tectonic event caused localized deformation. Estimated fault parameter indicates very shallow-dip reverse faulting in the uppermost crust, with a total seismic moment of 1.75E + 17 N m (Mw 5.4). This fault geometry is probably consistent with detachment structure indicated by geological studies. A simultaneous earthquake swarm with the maximum magnitude M4.1 suggests a possibility that the slow slip triggered the seismic activity for unknown reasons. This slow earthquake is slower than its moment would indicate, with a duration–magnitude scaling relationship unlike either regular earthquakes or subduction slow slip events. This result indicates that even if the area is under different physical property from subduction zones, slow earthquake can occur by some causes. Slow earthquakes exist in remote regions away from subduction zones and might play an important role in strain release and tectonic activity.

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.

Uncovering the physical controls of deep subduction zone slow slip using supervised classification of subducting plate features

2020 ◽  
Author(s):  
Morgan McLellan ◽  
Pascal Audet
Keyword(s):  
Subduction Zones ◽  
Weighted Average ◽  
Support Vector ◽  
Slow Slip ◽  
Sediment Thickness ◽  
Short Term ◽  
Linear Discriminant ◽  
Brittle Ductile Transition ◽  
Subducting Plate

Summary Deep slow slip events (SSEs) at subduction zones have significantly contributed to refining our understanding of the megathrust earthquake cycle at the brittle-ductile transition. However, the specific combination of factors that determine their occurrence has not yet been fully explored. Here we evaluate the contribution of several of these characteristics using globally mapped geophysical data that are used as proxies for physical properties of the subducting plate. This is performed by classifying 25 km-wide, trench-parallel segments into binary classes based on the observation (or lack thereof) of deep, short- or long-term SSEs. The five characteristics explored here include subducting plate age, sediment thickness, relative plate velocity, slab dip, and plate surface roughness. We use these characteristics to train six Machine Learning models based on different learning algorithms: Gaussian Naïve Bayes, Logistic Regression, Linear Discriminant Analysis, Random Forest, Support Vector Machine, and K-Nearest Neighbour. Short-term SSE models show that subducting plate age, relative velocity, and sediment thickness have the strongest predictive power with the first two characteristics negatively correlating and sediment thickness positively correlating with SSE occurrence, respectively. These results are consistent with a conceptual model where slow slip is controlled by conditions favoring the enduring release (and possible storage) of fluids near the source region. However, the relationship between these features and elevated pore fluid pressures is not established here and further evidence is needed to validate this hypothesis. We then use a final model constructed as a weighted average of the best performing models to make predictions on the probability of SSE occurrence, with predicted short-term SSE occurrence in South America, the Aleutians, Sumatra, Vanuatu and Solomon, as well as long-term SSE occurrence in the Aleutians, Izu-Bonin, Kuril-Kamchatka, Mariana, and Tonga-Kermadec. Overall, long-term SSE models do not perform as well as the short-term SSE models which may indicate that long-term SSEs are controlled by a different and/or extended set of physical characteristics than the short-term SSEs.

Build seismic cycle balance deformation with InSAR in Northen Chile

2020 ◽  
Author(s):  
Lauriane Bayle ◽  
Romain Jolivet ◽  
Nadaya Cubas ◽  
Laetitia Le Pourhiet
Keyword(s):  
Time Series ◽  
Subduction Zones ◽  
Permanent Deformation ◽  
Seismic Cycle ◽  
Seismic Displacement ◽  
Uplift Rates ◽  
Short And Long Term ◽  
Period Data ◽  
Illapel Earthquake

<p>Lauriane Baylé (1), Romain Jolivet (2), Nadaya Cubas (1) and Laetitia Le</p><p>Pourhiet (1)</p><p>(1) Institut des Sciences de la Terre de Paris, UMR 7193, UPMC UniversitéParis 6, CNRS, Paris,</p><p>France</p><p>(2) Laboratoire de Géologie, Département de Géosciences, École Normale Supérieure, CNRS UMR 8538,</p><p>PSL ResearchUniversity, Paris, France</p><p>Recent studies have pointed out to a discrepancy between the short- and long-</p><p>term deformation of overriding plates in subduction zones. This led to debates</p><p>about when and how permanent deformation is acquired. This contradiction</p><p>has notably been observed along the Central Andes Subduction Zone, where</p><p>the coast subsides during and shortly after major earthquakes while a coastal</p><p>uplift with rates ranging between 0.1 and 0.3 mm/yr has been inferred the</p><p>last 4000 ky. For instance, during the 15th September 2015 Mw 8.3 Illapel</p><p>earthquake the geodetics (GPS and InSAR) data show a coastal subsidence</p><p>along the line-of-sight of 20 cm in InSAR.</p><p>To reconcile the seemingly contradictory observations, we here propose to</p><p>provide a seismic cycle uplift balance by constrainning inter-, co- and post-</p><p>seismic vertical velocities from InSAR time series. The study focuses on La</p><p>Serena peninsula (71.3°W, 30°S, Chile) along which the Illapel earthquake</p><p>occurred and for which long-term uplift rates have been provided by previous</p><p>geomorphological studies.</p><p>To build this seismic cycle balance, we use InSAR data (Sentinel-1) acqui-</p><p>red between the September 15, 2015 and January 19, 2019. The time series</p><p>for the ascendant orbite is calculated and the accumulated vertical displace-</p><p>ment extracted providing co- and post-seismic displacement. The co-seismic</p><p>displacement are similar to those previously obtain. To constrain the displa-</p><p>cement during the inter-seismic period, data on both sides of the peninsula</p><p>are used. In that respect, we aim determining when, during the seismic cycle,</p><p>and where, along the coast, the uplift occurs.</p><p>The deduced time series will then be confronted to numerical modelling</p><p>to provide the short- and long-term mechanics reproducing the short- and</p><p>long-term observations.</p>

scholarly journals Effect of Ocean Fluid Changes on Pressure on the Seafloor: Ocean Assimilation Data Analysis on Warm-Core Rings off the Southeastern Coast of Hokkaido, Japan on an Interannual Timescale

2021 ◽  
Vol 9 ◽  
Author(s):  
Takuya Hasegawa ◽  
Akira Nagano ◽  
Keisuke Ariyoshi ◽  
Toru Miyama ◽  
Hiroyuki Matsumoto ◽  
...  
Keyword(s):  
Sea Surface ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Plate Convergence ◽  
Southeastern Coast ◽  
Warm Core ◽  
Slow Earthquakes ◽  
The Relationship ◽  
Interannual Scale

The relationship between sea surface height (SSH) and seawater density anomalies, which affects the pressure on the seafloor (PSF) anomalies off the southeastern coast of Hokkaido, Japan, was analyzed using the eddy-resolving spatial resolution ocean assimilation data of the JCOPE2M for the period 2001–2018. On an interannual (i.e., year-to-year) timescale, positive SSH anomalies of nearly 0.1 m appeared off the southeastern coast of Hokkaido, Japan, in 2007, associated with a warm-core ring (WCR), while stronger SSH anomalies (∼0.2 m) related to a stronger WCR occurred in 2016. The results show that the effects of such positive SSH anomalies on the PSF are almost canceled out by the effects of negative seawater density anomalies from the seafloor to the sea surface (SEP; steric effect on PSF) due to oceanic baroclinic structures related to the WCRs, especially in offshore regions with bottom depths greater than 1000 m. This means that oceanic isostasy is well established in deep offshore regions, compared with shallow coastal regions. To further verify the strength of the oceanic isostasy, oceanic isostasy anomalies (OIAs), which represent the barotropic component of SSH anomalies, are introduced and analyzed in this study. OIAs are defined as the sum of the SSH anomalies and SEP anomalies. Our results indicate that the effect of oceanic fluid changes due to SSH and seawater density anomalies (i.e., OIAs) on PSF changes cannot be neglected on an interannual timescale, although the amplitudes of the OIAs are nearly 10% of those of the SSH anomalies in the offshore regions. Therefore, to better estimate the interannual-scale PSF anomalies due to crustal deformation related to slow earthquakes including afterslips, long-term slow slip events, or plate convergence, the OIAs should be removed from the PSF anomalies.

scholarly journals Spatiotemporal Slip Distributions Associated with the 2018-2019 Bungo Channel Long-Term Slow Slip Event Inverted from GNSS Data

2021 ◽  
Author(s):  
Yukinari Seshimo ◽  
Shoichi Yoshioka
Keyword(s):  
Time Series ◽  
Time Series Data ◽  
Total Duration ◽  
Series Data ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Bungo Channel ◽  
Slip Event ◽  
Gnss Time Series

Abstract Long-term slow slip events (L-SSEs) have occurred beneath the Bungo Channel with durations of several months to a couple of years repeatedly with a recurrence interval of approximately six years. We estimated the spatiotemporal slip distributions of the 2018–2019 Bungo Channel L-SSE inverted from processed GNSS time series data. This event was divided into two subevents, with the first on the southwest side of the Bungo Channel from 2018.3 to 2018.7 and the second beneath the Bungo Channel from 2018.8 to 2019.4. Tectonic tremors became active on the downdip side of the L-SSE occurrence region when large slow slips took place beneath the Bungo Channel. Compared with the previous Bungo Channel L-SSEs, this spatiotemporal slip pattern and amount were similar to those of the 2003 L-SSE. However, the slip expanded in the northeast-southwest direction in the latter half of the second subevent. We also found that the total duration of the two subevents was 1.0 year, which was the shortest among the four recent L-SSEs beneath the Bungo Channel identified using GNSS time series data. The maximum amount of slip, the maximum slip velocity, the total released seismic moment, and the moment magnitude of the 2018–2019 L-SSE were estimated to be 27 cm, 53 cm/year, 4.1×1019 Nm, and 7.0, respectively, all of which were the largest among the four L-SSEs.

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.

scholarly journals Aerosol optical depth retrievals at the Izaña Atmospheric Observatory from 1941 to 2013 by using artificial neural networks

2016 ◽  
Vol 9 (1) ◽  
pp. 53-62 ◽  
Author(s):  
R. D. García ◽  
O. E. García ◽  
E. Cuevas ◽  
V. E. Cachorro ◽  
A. Barreto ◽  
...  
Keyword(s):  
Neural Networks ◽  
Time Series ◽  
Artificial Neural Networks ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Mineral Dust ◽  
Dust Particles ◽  
Filter Radiometer ◽  
Artificial Neural

Abstract. This paper presents the reconstruction of a 73-year time series of the aerosol optical depth (AOD) at 500 nm at the subtropical high-mountain Izaña Atmospheric Observatory (IZO) located in Tenerife (Canary Islands, Spain). For this purpose, we have combined AOD estimates from artificial neural networks (ANNs) from 1941 to 2001 and AOD measurements directly obtained with a Precision Filter Radiometer (PFR) between 2003 and 2013. The analysis is limited to summer months (July–August–September), when the largest aerosol load is observed at IZO (Saharan mineral dust particles). The ANN AOD time series has been comprehensively validated against coincident AOD measurements performed with a solar spectrometer Mark-I (1984–2009) and AERONET (AErosol RObotic NETwork) CIMEL photometers (2004–2009) at IZO, obtaining a rather good agreement on a daily basis: Pearson coefficient, R, of 0.97 between AERONET and ANN AOD, and 0.93 between Mark-I and ANN AOD estimates. In addition, we have analysed the long-term consistency between ANN AOD time series and long-term meteorological records identifying Saharan mineral dust events at IZO (synoptical observations and local wind records). Both analyses provide consistent results, with correlations  >  85 %. Therefore, we can conclude that the reconstructed AOD time series captures well the AOD variations and dust-laden Saharan air mass outbreaks on short-term and long-term timescales and, thus, it is suitable to be used in climate analysis.

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