ALBERT

Description: This data set includes digital image correlation data from thirteen analogue earthquakes generated by means of an analogue seismotectonic scale model approach. The data consists of grids of 3D static coseismic surface displacements. The data have been derived using a stereo camera setup and processed with LaVision Davis 8 software. Detailed descriptions of the experiments and results regarding the control of geodetic coverage on the slip inversion problem can be found in Kosari et al. (in review) to which this data set is supplementary material. We use an analogue seismotectonic scale model approach (Rosenau et al., 2017) to generate a catalogue of analogue megathrust earthquakes (Table 1). The presented experimental setup is modified from the 3D setup used in Rosenau et al. (2019). To monitor surface deformation of the wedge analogue model a stereoscopic set of two CCD cameras (LaVision Imager pro X 11MPx, 14 bit) monitors images the wedge surface continuously at 2.5 Hz. To derive observational data similar to those from geodetic techniques, i.e. velocities at the location on the surface, we use digital image correlation (DIC, Adam et al., 2005) to derive the 3D incremental surface displacement (or velocity) at high spatial resolution (〈 0.1 mm). The time series of incremental surface displacement data was calculated using LaVision Davis 8 software. The result is an evenly spaced grid of vectors per time step, oriented parallel with respect to the principal dimensions of the box.

Description: This dataset provides friction and elasticity data from ring shear and axial tests, respectively, on rock analogue materials used at the University Roma Tre (Rome, IT) in “Foamquake”, a novel seismotectonic analog model mimicking the megathrust seismic cycle (Mastella et al., under review). Two granular materials (quartz sand and Jasmine rice) have been characterized by means of internal friction coefficients µ and cohesions C. An elastic material (foam rubber) have been characterized by means of Young’s modulus E and Poisson’s ratio v. According to our analysis the granular materials show Mohr-Coulomb behaviour characterized by linear failure envelopes in the shear stress vs. normal load Mohr space. Peak, dynamic and reactivation friction coefficients of the quartz sand are µP = 0.69, µD = 0.56 and µR = 0.64, respectively. Cohesion ranges between 50 and 100 Pa. Rate-dependency of friction in quartz sand seems insignificant. Peak, dynamic and reactivation friction coefficients of the Jasmine rice are µP = 0.70, µD = 0.59 and µR = 0.61, respectively. Cohesion ranges between 30 and 50 Pa. Rate-weakening of Jasmine rice is c. 6% per tenfold change in shear velocity v. The Young’s modulus of the foam rubber has been constrained to 30 kPa, its Poisson’s ratio is v=0.1.

Description: Subduction zones, where one tectonic plate slides underneath the other, host the largest earthquakes on Earth. These zones are characterized by intense earthquake activity and are responsible for 95 % of all moment releases on Earth. The shallow portion of the subduction zone interface (i.e., megathrust) generated the largest ever recorded earthquakes, such as the 1960 Valdivia earthquake in Chile, the 2004 Sumatra earthquake in Indonesia, and the 2011 Tohoku-Oki earthquake in Japan on the Earth. Unwrapping the behavior of this portion of the subduction zone, which generates the most significant earthquakes and devastating tsunamis, is a vital step forward in earthquake geoscience. Monitoring only a fraction of a single megathrust earthquake cycle and the offshore location of the source of these earthquakes are the foremost reasons for the insufficient understanding. The insufficient offshore observation and the interseismic data incompleteness led earthquake scientists to employ analog and numerical modeling approaches to unfold the linkage between short-term elastic (i.e., coseismic) and long-term permanent (i.e., several seismic cycles) deformation of the subduction zones. Revealing these relationships allows us to identify which long and short-term signals earthquake scientists should look for remotely or in the field to unwrap the subduction zone’s seismic cycle history. In this research, I investigate a simplified analog model of a subduction zone from trench to the location of volcanic arc and 240 km along strike using elastoplastic granular material and stick-slip analog material at a laboratory scale. Establishing generic seismotectonic scale models enables me to generate hundreds of megathrust seismic cycles and monitor the earthquake-related surface and cross-sectional deformation pattern at high resolution in both space and time. I attempt to demonstrate what surface deformation signals the frictional and mechanical changes on the interface generates over coseismic and early postseismic stages and interseismic intervals. Additionally, at a more extended time scale (tens to hundreds of earthquake cycles), I study what surface strain pattern in the forearc from the trench to the coastal region can be permanently preserved. This provides critical observations for earthquake geoscientists to tie forearc surface deformation to subsurface elastoplastic processes at the shallow portion of the subduction interface. I apply a geodetic slip inversion technique to analog trench-breaking and non-trench-breaking megathrust earthquakes to demonstrate how limited offshore geodetic coverage affects coseismic slip models. The slip models derived from analog earthquakes show quantitative and qualitative changes as a function of offshore coverage: 1) Shallow slip cannot be resolved if the observation coverage of the offshore segment is 〈50%. 2) the slip pattern of shallow event flips from landward to trenchward skewed as offshore coverage reduces to 〈40%. 3) In the case of no offshore coverage, the slip pattern for both event types converges to a similar unimodal pattern. Additionally, I infer 5-20% slip overestimation when the observations are above the high slipping zone during trench-breaking events versus 5-10% underestimation during non-trench-breaking events if observations are land-limited. Moreover, the moment magnitude derived for trench-breaking ruptures might be affected. Furthermore, I mimic homogenous and heterogeneous megathrust interfaces at the laboratory scale to monitor the strain relaxation on the two elastically non-identical plates by establishing analog velocity weakening and strengthening materials. I propose a sequential elastic rebound that follows the coseismic shear-stress drop in the elastic-frictional models: a fast rebound of the upper plate and the delayed and smaller rebound on the slab. The delayed rebound of the slab, along with the rapid relaxation of the upper plate after an elastic overshooting, accelerates the relocking of the megathrust. This acceleration triggers/antedates the failure of a nearby asperity and enhances the early backslip in the rupture area. The long-term frictional-elastoplastic interaction between the interface and its overlying wedge causes variable surface strain signals. I establish two coseismically compressional and extensional wedge configurations to explore the mechanical and kinematic interaction between the shallow wedge and the interface. The results demonstrate that this interaction can partition the wedge into different segments. I highlight that a more segmented upper plate represents a subduction megathrust that generates more characteristic and periodic events. Moreover, the results illustrate that different wedge segments may switch their state from compression/extension to extension/compression domains. Additionally, the strain time series of the coastal zone reveals that the strain state may remain quasi-stable over a few seismic cycles before switching to the opposite mode. These observations are key for evaluating earthquake-related morphotectonic markers (i.e., marine terraces) and short-term interseismic GPS time-series onshore (coastal region).

Description: In Subduktionszonen, in denen sich eine tektonische Platte unter die andere schiebt, ereignen sich die größten Erdbeben der Erde. Diese Zonen zeichnen sich durch eine starke Erdbebentätigkeit aus und sind für 95 % der Energiefreisetzung durch Erdbeben auf der Erde verantwortlich. Der obere Teil der Subduktionszone (d. h. die Megathrust) erzeugte die größten jemals aufgezeichneten Erdbeben wie das Valdivia-Erdbeben von 1960 in Chile, das Sumatra-Erdbeben von 2004 in Indonesien und das Tohoku-Oki-Erdbeben von 2011 in Japan. Die Entschlüsselung des Verhaltens dieses Teils der Subduktionszone, der die bedeutendsten Erdbeben und verheerenden Tsunamis hervorruft, ist ein entscheidender Schritt nach vorn in der Erdbebengeowissenschaft. Die Beobachtung von nur einem Bruchteil eines einzelnen Megathrust-Erdbebenzyklus und die Offshore-Lage der Quelle dieser Erdbeben sind die Hauptgründe für das unzureichende Verständnis. Die unzureichende Offshore-Beobachtung und die Unvollständigkeit der interseismischen Daten haben die Erdbebenforscher dazu veranlasst, analoge und numerische Modellierungsansätze anzuwenden, um den Zusammenhang zwischen kurzfristiger elastischer (d. h. koseismischer) und langfristiger permanenter (d. h. mehrere seismische Zyklen umfassender) Verformung der Subduktionszonen aufzudecken. Die Aufdeckung dieser Beziehungen ermöglicht es uns, zu ermitteln, nach welchen lang- und kurzfristigen Signalen Erdbebenforscher suchen sollten, um die seismische Zyklusgeschichte der Subduktionszone zu entschlüsseln. In dieser Forschungsarbeit untersuche ich ein vereinfachtes analoges Modell einer Subduktionszone vom Tiefseegraben bis zum Vulkanbogen und etwa 240 km entlang des Streichens der Subduktionszone unter Verwendung von elastoplastischem granularem Material und analogem Stick-Slip-Material im Labormaßstab. Die Erstellung allgemeiner seismotektonischer Modelle ermöglicht es mir, Hunderte von seismischen Megathrust-Erdbebenzyklen zu erzeugen und die erdbebenbedingten Oberflächen- und Querschnittsverformungsmuster mit hoher räumlicher und zeitlicher Auflösung zu überwachen. Ich versuche zu demonstrieren, welche Oberflächendeformationssignale die Reibung und die mechanischen Veränderungen an der Grenzfläche über koseismische und frühe postseismische Phasen und interseismische Intervalle hinweg erzeugen. Darüber hinaus untersuche ich auf einer längeren Zeitskala (Dutzende bis Hunderte von Erdbebenzyklen), welche Oberflächendeformationsmuster im Forearc, vom Graben bis zur Küstenregion, dauerhaft erhalten werden können. Dies liefert den Erdbebengeowissenschaftlern wichtige Beobachtungen, um die Oberflächendeformation des Plattenrandes mit den elastoplastischen Prozessen unter der Oberfläche im flachen Teil der Subduktionsgrenze zu verbinden. Ich wende eine geodätische Inversionstechnik zur Ableitung des koseismischen Versatzes entlang der Megathrust auf analoge grabenbrechende und nicht grabenbrechende Megathrust Erdbeben an, um zu demonstrieren, wie eine begrenzte geodätische Offshore-Abdeckung koseismische Versatzmodelle beeinflusst. Die aus analogen Erdbeben abgeleiteten Versatzmodelle zeigen quantitative und qualitative Veränderungen in Abhängigkeit von der Offshore-Abdeckung: 1) Flacher Versatzkann nicht aufgelöst werden, wenn die Beobachtungsabdeckung des Offshore-Segments 〈50% ist. 2) Das Versatzsmuster eines flachen Ereignisses kippt von landwärts zu grabenwärts vergent, wenn die Offshore-Abdeckung auf 〈40% sinkt. 3) Im Falle keiner küstennahen Abdeckung konvergiert das Versatzmuster für beide Ereignistypen zu einem ähnlichen unimodalen Muster. Darüber hinaus schließe ich auf eine 5-20%ige Überschätzung des Versatzes, wenn die Beobachtungen oberhalb der flachen Versatzzone während grabenbrechenden Ereignissen liegen, gegenüber einer 5-10%igen Unterschätzung während nicht grabenbrechenden Ereignissen, wenn die Beobachtungen landgebunden sind. Außerdem kann die für grabenbrechende Brüche abgeleitete Momentgröße beeinflusst werden. Darüber hinaus ahme ich homogene und heterogene Megathrust-Grenzflächen im Labormaßstab nach, um die Dehnungsrelaxation an den beiden elastisch nicht identischen Platten zu überwachen, indem ich analoge Materialien einsetze, die ratenabhängige Festigkeiten zeigen. Ich schlage einen sequentiellen elastischen Rebound vor, der dem koseismischen Scherspannungsabfall in den elastischen Reibungsmodellen folgt: einen schnellen Rebound der oberen Platte und den verzögerten und kleineren Rebound an der abtauchenden Platte. Der verzögerte Rebound der abtauchenden Platte, zusammen mit der schnellen Entspannung der oberen Platte nach einem elastischen Überschießen, beschleunigt die Wiederkopplung der Megathrust. Diese Beschleunigung löst/begünstigt das Versagen einer nahe gelegenen Asperity und verstärkt das frühe Rückgleiten im Bruchbereich. Die langfristige reibungs-elastoplastische Wechselwirkung zwischen der Grenzfläche und dem darüber liegenden Keil verursacht variable Oberflächendehnungssignale. Ich habe zwei Keilkonfigurationen mit koseismischer Kompression und Dehnung erstellt, um die mechanische und kinematische Wechselwirkung zwischen dem flachen Keil und der Grenzfläche zu untersuchen. Die Ergebnisse zeigen, dass diese Wechselwirkung den Keil in verschiedene Segmente aufteilen kann. Ich hebe hervor, dass eine stärker segmentierte obere Platte eine Subduktions-Megathrust darstellt, die mehr charakteristische und periodische Ereignisse erzeugt. Darüber hinaus veranschaulichen die Ergebnisse, dass verschiedene Keilsegmente ihren Zustand von Kompressions-/Dehnungs- zu Extensions-/Kompressionsbereichen wechseln können. Darüber hinaus zeigt die Zeitreihe der Dehnungen in der Küstenzone, dass der Dehnungszustand über einige seismische Zyklen quasistabil bleiben kann, bevor er in einen entgegengesetzten Verkürzuungs-Modus übergeht. Diese Beobachtungen sind von entscheidender Bedeutung für die Bewertung erdbebenbedingter morphotektonischer Marker (z. B. Meeresterrassen) und kurzfristiger interseismischer GPS-Zeitserien an Land (Küstenregion).

Description: This data set includes digital image correlation data from analog earthquakes experiments. The data consists of grids of surface strain and time series of surface displacement (horizontal and vertical) and strain. The data have been derived using a stereo camera setup and processed with LaVision Davis 10 software. Detailed descriptions of the experiments and results regarding the surface pattern of the strain can be found in Kosari et al. (in review), to which this data set is supplementary. We use an analog seismotectonic scale model approach (Rosenau et al., 2019 and 2017) to generate a catalog of analog megathrust earthquakes (Table 1). The presented experimental setup is modified from the 3D setup used in Rosenau et al. (2019) and Kosari et al. ( 2020). The subduction forearc model wedge is set up in a glass-sided box (1000 mm across strike, 800mm along strike, and 300 mm deep) with a dipping, elastic basal conveyor belt and a rigid backwall. An elastoplastic sand-rubber mixture (50 vol.% quartz sandG12: 50 vol.% EPDM rubber) is sieved into the setup representing a 240 km long forearc segment from the trench to the volcanic arc. The shallow part of the wedge includes a basal layer of sticky rice grains characterized by unstable stick-slip sliding representing the seismogenic zone. Stick-slip sliding in rice is governed by a rate-and-state dependent friction law similar to natural rocks. According to Coulomb wedge theory (Dahlen et al., 1984), two types of wedge configurations have been designed: a “compressional” configuration represents an interseismically compressional and coseismically stable wedge (compressional configuration), and a “critical” configuration, which is interseismically stable (close to critically compressional) and may reach a critical extensional state coseismically (critical configuration). In the compressional configuration, a flat-top (surface slope α=0) wedge overlies a single large rectangular in map view stick-slip patch (Width*Length=200*800 mm) over a 15-degree dipping basal thrust. In the critical configuration, the surface angle of the elastoplastic wedge varies from the coastal segment onshore (α=10) to the inner-wedge offshore (α=15) segments over a 5-degree dipping basal thrust. Slow continuous compression of the wedge by moving the basal conveyor belt at a speed velocity of 0.05 mm/s simulates plate convergence and results in the quasi-periodic nucleation of quasi-periodic stick-slip events (analog earthquakes) within the rice layer. The wedge responds elastically to these basal slip events, similar to crustal rebound during natural subduction megathrust earthquakes.

Description: This dataset provides friction data from ring-shear tests (RST) on twice broken rice used in the GEC Laboratory in CY Cergy Paris University in stick-slip experiments. They were obtained by Sarah Visage as part of her doctoral training (funded by the ANR DISRUPT programme) during an invitation at the Helmholtz Laboratory for Tectonic Modelling (HelTec) at the GFZ German Research Centre for Geosciences in Potsdam. Like any granular material, the twice broken rice is characterized by several internal friction coefficients μ and cohesions C, classicaly qualified as dynamic, static, and reactivation coefficients. In adition, since the rice exhibits a stick slip behaviour, the various shear - velocity or shear-displacement curves exhibit high frequency oscillations and we therefore define maximum, minimum, and mean values corresponding respectively to the curve peaks, curve troughs and smoothed curve.

Description: An earthquake-induced stress drop on a megathrust instigates different responses on the upper plate and slab. We mimic homogenous and heterogeneous megathrust interfaces at the laboratory scale to monitor the strain relaxation on two elastically bi-material plates by establishing analog velocity weakening and neutral materials. A sequential elastic rebound follows the coseismic shear-stress drop in our elastoplastic-frictional models: a fast rebound of the upper plate and the delayed and smaller rebound on the elastic belt (model slab). A combination of the rebound of the slab and the rapid relaxation (i.e., elastic restoration) of the upper plate after an elastic overshooting may accelerate the relocking of the megathrust. This acceleration triggers/antedates the failure of a nearby asperity and enhances the early slip reversal in the rupture area. Hence, the trench-normal landward displacement in the upper plate may reach a significant amount of the entire interseismic slip reversal and speeds up the stress build-up on the upper plate backthrust that emerges self-consistently at the downdip end of the seismogenic zones. Moreover, the backthrust switches its kinematic mode from a normal to reverse mechanism during the coseismic and postseismic stages, reflecting the sense of shear on the interface.

Description: This data set includes data derived from high-speed surface displacement observations from analog earthquake experiments. The data consists of surface displacement of the experiment upper plate and slab, slip distribution, and grids of Coulomb Failure Stress (CFS). The surface displacement observations have been captured using a highspeed CMOS (Complementary Metal Oxide Semiconductor) camera (Phantom VEO 640L camera, 12 bit) and processed with LaVision Davis 10 software. Description of the experiments and results regarding the surface displacement observation, Slip distribution, and CFS can be found in Kosari et al. (2022), to which this data set is supplementary. We use an analog seismotectonic scale model approach (Rosenau et al., 2019 and 2017) to generate a catalog of analog megathrust earthquakes. The presented experimental setup is modified from the 3D setup used in Rosenau et al. (2019) and Kosari et al. ( 2020 and 2022). The subduction forearc model wedge is set up in a glass-sided box (1000 mm across strike, 800mm along strike, and 300 mm deep) with a dipping, elastic basal conveyor belt, and a rigid backwall. An elastoplastic sand-rubber mixture (50 vol.% quartz sandG12: 50 vol.% EPDM rubber) is sieved into the setup representing a 240 km long forearc segment from the trench to the volcanic arc. The shallow part of the wedge includes a basal layer of sticky rice grains characterized by unstable stick-slip sliding representing the seismogenic zone. The Stick-slip sliding in rice is governed by a rate-and-state dependent friction law similar to natural rocks. A flat-top (surface slope α=0) wedge overlies rectangular stick-slip patch/es over a 15-degree dipping basal thrust. Two different seismic configurations of the shallow part of the wedge base (the megathrust) represent the depth extent of the seismogenic zone in nature. In the first configuration (homogeneous configuration), a single large rectangular stick-slip patch (Width*Length=200*800 mm) is implemented as the main slip patch (MSP). In the second case (heterogeneous configuration), two square-shaped MSPs (200*200mm) have been emplaced, acting as two medium-size seismogenic asperities surrounded by a salt matrix hosting frequent small events. Slow continuous compression of the wedge by moving the basal conveyor belt at a speed velocity of 0.05 mm/s simulates plate convergence and results in the quasi-periodic nucleation of quasi-periodic stick-slip events (analog earthquakes) within the sticky-rice layer. The wedge responds elastically to these basal slip events, similar to crustal rebound during natural subduction megathrust earthquakes.

Description: A triplet of Mw ∼6 earthquakes on 2017 December 1–12 occurred ∼50 km north of Kerman, Iran, in an area of mountainous topography where several major right-lateral strike-slip fault systems—the Gowk, Nayband, Lakar Kuh and Kuh Banan faults—converge. Here we assess their source parameters and surficial expression using regional and teleseismic waveforms and arrival times, synthetic aperture radar interferometry, optical satellite image correlation and field observations. All three main shocks occurred on shallow reverse faults associated with the southern termination of the Lakar Kuh right-lateral strike-slip fault. The first two main shocks on 1 December and 12 December (08:43 UTC) likely ruptured and reruptured a previously unrecognized, blind, NE-dipping fault beneath the Mian Kuh range. Slip in both earthquakes extends much further along strike than down dip, hinting at structural or stratigraphic controls on rupture dimensions. The third main shock on 12 December (21:41 UTC) is perhaps the most interesting of the three events. It ruptured a conjugate SW-dipping thrust in the hangingwall of the first fault, generating a sinuous fault scarp in the alluvial plain north of the Mian Kuh range, consistent with its unusually shallow centroid depth of ∼2 km. Its high ratio of net surface slip (average ∼1.5 m and maximum ∼2.5 m) to length (∼7 km) and its narrow down-dip width (∼6 km) implies a very high stress drop. The surface rupture aligns along-strike with larger scarps that contain uplifted and incised fan surfaces in their hangingwalls, but this subtle expression of active faulting had not been fully recognized prior to these earthquakes. The clustering in space and time of large, shallow earthquakes on hidden faults is of broad concern for seismic hazard assessment in mountainous parts of Iran and in other collisional settings.