slip deficit
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2021 ◽  
Author(s):  
Nadaya Cubas ◽  
Philippe Agard ◽  
Roxane Tissandier

Abstract. What controls the location and segmentation of mega-earthquakes in subduction zones is a long-standing problem in earth sciences. Prediction of earthquake ruptures mostly relies on interplate coupling models based on Global Navigation Satellite Systems providing patterns of slip deficit between tectonic plates. We here investigate if and how the seismic and aseismic patches revealed by these models relate to the distribution of deformation along the plate interface, i.e. basal erosion and/or underplating. From a mechanical analysis of the topography applied along the Chilean subduction zone, we show that extensive plate interface deformation takes place along most of the margin. We show that basal erosion occurs preferentially at 15 km depth while underplating does at 35 ± 10 and 60 ± 5 km depth, in agreement with P-T conditions of recovered underplated material, expected pore pressures, and spatial distribution of marine terraces and uplift rates. Along southern Chile, large sediment input favors shallow accretion and underplating of subducted sediments, while along northern Chile, extensive basal erosion provides material for the underplating. We then show that all major earthquakes of southern Chile are limited along their down-dip end by underplating while, along northern Chile, they are surrounded by both basal erosion and underplating. Segments with heterogeneously distributed deformation largely coincide with lateral earthquake terminations. We therefore propose that long-lived plate interface deformation promotes stress build-up and leads to earthquake nucleation. Earthquakes then propagate along fault planes shielded from this long-lived permanent deformation, and are finally stopped by segments of heterogeneously distributed deformation. Slip deficit patterns and earthquake segmentation therefore reflect the along-dip and along-strike distribution of the plate interface deformation. Topography acts as a mirror of distributed plate interface deformation and should be studied systematically to improve the prediction of earthquake ruptures.


2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Masayuki Kano ◽  
Aoi Ikeuchi ◽  
Takuya Nishimura ◽  
Shin’ichi Miyazaki ◽  
Takeshi Matsushima

AbstractThe southern part of the Ryukyu subduction zone has recorded tsunami events with a recurrence interval of several hundred years. Although their source is controversial, one model suggests that the last 1771 Yaeyama tsunami was caused by a shallow megathrust earthquake with a magnitude of 8. However, the current knowledge on interplate coupling based on recent geodetic data is limited. Here, a time series of Global Navigation Satellite System data from January 2010 to February 2021 was analyzed, including newly installed stations by Kyoto and Kyushu Universities, to obtain the distance changes between stations and vertical secular velocities. The distance changes ranged from 2.4 mm/year in contraction and to 4.7 mm/year in extension, and the vertical velocities exhibited no clear uplift or subsidence, with − 2.4 to 1.1 mm/year. The back slip inversion results indicated a slip deficit of 17–47 mm/year to the south of the Yaeyama Islands. The large slip deficit area is complementarily intervened between the shallower source area of low-frequency earthquakes and the deeper slow slip region, suggesting the spatial heterogeneity of frictional properties along the plate interface. If the large slip deficit area accumulates stress in the same rate since the last 1771 earthquake, it could result in a megathrust event with a moment magnitude greater than 7.5. Because the limited onshore data cannot resolve the slip deficit on the shallow plate interface, seafloor geodetic observations are essential to clarify the detailed spatial distribution of the slip deficit and discuss its earthquake and tsunami potential. Graphical Abstract


2021 ◽  
Author(s):  
Masayuki Kano ◽  
Aoi Ikeuchi ◽  
Takuya Nishimura ◽  
Shin'ichi Miyazaki ◽  
Takeshi Matsushima

Abstract The southern part of the Ryukyu subduction zone has recorded tsunami events with a recurrence interval of several hundred years. Although their source is controversial, one model suggested that the last 1771 Yaeyama tsunami was caused by a shallow megathrust earthquake with a magnitude of 8. However, the current knowledge on interplate coupling based on recent geodetic data is limited. This study analyzed a time series of Global Navigation Satellite System data from January 2010 to February 2021, including newly installed stations by Kyoto and Kyushu Universities to obtain the distance changes between stations and vertical secular velocities. The distance changes ranged 2.4 mm/yr in contraction and 4.7 mm/yr in extension, and the vertical velocities exhibited no clear uplift or subsidence of -2.4 to 1.1 mm/yr. The back slip inversion results indicated the slip deficit of 16–54 mm/yr in the south of the Yaeyama Islands. The large slip deficit area is complementarily intervened between the shallower source area of low-frequency earthquakes and the deeper slow slip region, suggesting the spatial heterogeneity of frictional properties along the plate interface. If the large slip deficit area accumulates stress in the same rate since the last 1771 earthquake, it could result in a megathrust event of at least greater than a moment magnitude of 7.7. Because the limited onshore data cannot resolve the slip deficit on the shallow plate interface, seafloor geodetic observations are essential to clarify the detailed spatial distribution of slip deficit and discuss its earthquake and tsunami potential.


2021 ◽  
Vol 7 (1) ◽  
pp. 1-10
Author(s):  
Tara Adventari ◽  
Widodo Setyo Pranowo ◽  
Dian Adrianto ◽  
Muhammad Ramdhan ◽  
Johar Setiyadi

Dari hasil relokasi kejadian gempa yang tercatat oleh Badan Meteorologi, Klimatologi, dan Geofisika (BMKG) dan inversi data Global Positioning System (GPS) menunjukkan bahwa terdapat celah seismik (seismic gaps) di selatan Jawa, yaitu wilayah di sepanjang batas lempeng aktif yang tidak mengalami gempa besar atau gempa selama lebih dari 30 tahun. Pada zona tersebut diperkirakan terjadi penguncian (locked) terhadap pergeseran lempeng (slip deficit) yang berakibat pada akumulasi pengumpulan energi dan berpotensi menimbulkan gempa megathrust yang bersifat tsunamigenik. Pada penelitian ini dilakukan pemodelan numerik tsunami menggunakan persamaan gelombang shallow water 2 dimensi dengan 3 skenario gempa megathrust akibat patahnya lempeng samudera di zona celah seismik selatan Jawa. Skenario patahan lempeng di selatan Jawa Barat menyebabkan gempa dengan Mw 8,9, di selatan Jawa Tengah dan Jawa Timur sebesar Mw 8,8, dan untuk skenario patahan dari Jawa Barat sampai Jawa Timur sebesar Mw 9,1. Dari hasil simulasi selama 10 jam menggunakan software TUNAMI N2, dihasilkan gelombang tsunami setinggi maksimum 6 meter di pesisir selatan Jawa untuk gempa berkekuatan Mw 8,9, 12 meter untuk gempa berkekuatan Mw 8,8,  dan 20 meter untuk gempa berkekuatan Mw 9,1. Propagasi dan travel time tsunami diamati oleh outlet-outlet ARLINDO berupa shallow pressure gauge (SPG) yang ditempatkan di jalur-jalur ARLINDO.


2021 ◽  
Vol 9 ◽  
Author(s):  
Sota Murakami ◽  
Tsuyoshi Ichimura ◽  
Kohei Fujita ◽  
Takane Hori ◽  
Yusaku Ohta

Estimating the coseismic slip distribution and interseismic slip-deficit distribution play an important role in understanding the mechanism of massive earthquakes and predicting the resulting damage. It is useful to observe the crustal deformation not only in the land area, but also directly above the seismogenic zone. Therefore, improvements in terms of measurement precision and increase in the number of observation points have been proposed in various forms of seafloor observation. However, there is lack of research on the quantitative evaluation of the estimation accuracy in cases where new crustal deformation observation points are available or when the precision of the observation methods have been improved. On the other hand, the crustal structure models are improving and finite element analysis using these highly detailed crustal structure models is becoming possible. As such, there is the real possibility of performing an inverted slip estimation with high accuracy via numerical experiments. In view of this, in this study, we proposed a method for quantitatively evaluating the improvement in the estimation accuracy of the coseismic slip distribution and the interseismic slip-deficit distribution in cases where new crustal deformation observation points are available or where the precision of the observation methods have been improved. As a demonstration, a quantitative evaluation was performed using an actual crustal structure model and observation point arrangement. For the target area, we selected the Kuril Trench off Tokachi and Nemuro, where M9-class earthquakes have been known to occur in the past and where the next imminent earthquake is anticipated. To appropriately handle the effects of the topography and plate boundary geometry, a highly detailed three-dimensional finite element model was constructed and Green’s functions of crustal deformation were calculated with high accuracy. By performing many inversions via optimization using Green’s functions, we statistically evaluated the effect of increase in the number of observation points of the seafloor crustal deformation measurement and the influence of measurement error, taking into consideration the diversity of measurement errors. As a result, it was demonstrated that the observation of seafloor crustal deformation near the trench axis plays an extremely important role in the estimation performance.


2021 ◽  
Author(s):  
Alison Seidel ◽  
Henriette Sudhaus

<p>Crustal earthquakes are events of sudden stress release throug­h rock failure, for example as a consequence of continuous and long-term stress buildup at tectonic faults that eventually exceeds the strength of rock. Before failure, under increasing stress at a fault, the surrounding crust is slowly deforming. The amount and pattern of crustal deformation carries information about location and potential magnitude of future earthquakes.</p><p>Time series of space-borne interferometric Synthetic Aperture Radar (InSAR) data can be used to precisely measure the surface motion, which corresponds to the crustal deformation, in the radar line-of-sight and across large areas. These observations open the opportunity to study fault loading in terms of location, size of locked parts at faults and their slip deficit. Here we study the North Anatolian Fault (NAF), a major right-lateral strike-slip fault zone of about 1500 km length in the north of Turkey and we create its first large-scale 3D finite-fault model based on InSAR data.</p><p>We use the InSAR time series of data recorded by ESA’s Envisat SAR satellite between 2002 and 2010 (Hussain et al., 2018 and Walters et al., 2014).<!-- Das ist nicht ganz eindeutig formuliert. rigid motion darf nicht auf die InSAR Daten bezogen werden. --> We represent the fault with several vertical, planar fault segments that trace the NAF with reasonable resolution. The medium model is a layered half space with a viscoelastic lower crust and mantle. Several GNSS velocity measurements are used to apply a trend correction and calibrate the InSAR time series data to an Eurasia-fixed-reference frame. We use the plate motion difference of the Anatolian and the Eurasian plates calculated through an Euler pole to set up a back-slip finite-fault model. We then optimize the back-slip as the slip deficit, the width and the depth of the locked fault zone at each segment to achieve a good fit to the measured surface motion.</p><p>We find shallow locking depths and small slip deficits in the eastern and westernmost regions of the NAF, while the central part shows both deeper locking depths and larger slip deficits for the observation period. <!-- So wie es jetzt ist sind es zu viele Wörter, wenn man diesen erklär-Satz rausnehmen würde, würde es gerade so passen. Für die Erdbebenaktivität im Osten hab ich bis jetzt für den Zeitraum auch noch kein entsprechendes Paper gefunden, da suche ich aber noch. -->For both parameters the trends are in an overall agreement to earlier studies. There, InSAR-time series data have been used to calculate slip deficits at the North Anatolian fault with 2D models and/or assuming a homogeneous and purely elastic medium.<!-- Passt vom flow jetzt besser hier hin, denke ich. --> Local modeled differences therefore might be connected to differences in the modeling approaches, but also remain subject to further investigations and discussions.</p><p>Our model provides a very suitable basis for future time-dependent modeling of the slip deficit at the NAF that includes also more recent InSAR time series based on data from the Sentinel-1 radar satellite mission of ESA.</p>


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