Bridging the scales: Short- to long-term deformation signals from a laboratory subduction megathrust

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).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)

Thirdspace: the Trialectics of the Real, Virtual and Blended Spaces

This article aims to redefine the concept of Thirdspace and make a trilateral relationship between the three concepts of real space, virtual space and the user. To do so, not only the concept of Thirdspace has to be redefined, but also a new understanding of virtual space as a relatively independent space is required. This three-sided relation requires a new understanding of the relationship between the body and virtual space. Special attention is paid to the role of the body in the relationship between the user and virtual space through a phenomenological approach. Borderline spaces - VR technology and video games such as Pokémon Go - which are resulted from the interpenetration of real and virtual spaces have been considered as the new edges of interaction between real and virtual spaces and they are on a constant rise. This article's key question is if using the concept of Thirdspace, one could build a bridge on the theoretical gap between real and virtual spaces and better understand the confrontation of the user with real, virtual and borderline spaces as well as their lived experiences. The authors believe that the answers are positive. This understanding paves the way not only to help the users improve their life skills for today's real-virtual world but also to manage the stresses caused by living in such surroundings

How Iranian Women Express Themselves through Social Media Photos: a Case Study of Instagram

In this study, the issue of using Instagram social network by different groups of Iranian women and their interests and desires in publication of photos is investigated. The purpose of the study is to identify the common aspects and differences in women's lives reflected in their self-expression efforts based on their social characteristics. Therefore, the women were classified into eight groups based on the elements affecting the way they show their daily lives, such as education level, occupation and marital status. Then, qualitative method, including virtual ethnographic techniques, content analysis and online interviews, was used. Photos posted on Instagram by 32 users were studied and analyzed, and these users were interviewed. Questions were asked about their tendency towards posting photos of their daily lives on Instagram via direct messages. The conceptual framework of the study included Bourdieu’s theory of 'distinction' and Baudrillard’s concept of 'system of objects'. Results showed that women in each group select specific approaches to the publication of photos based on their social conditions. In the present article, these differences are discussed in detail. The significance of this research lies in the possibility of understanding different aspects of women’s everyday life and their individual identity through self-reports in the new media as opposed to the traditional media which only presents a standardized type of identification. Since studying women's efforts in presenting themselves on social media has been neglected in studies conducted on social networks in Iran, this study leads to a better understanding of Iranian women's diverse identities

Strain Signals Governed by Frictional‐Elastoplastic Interaction of the Upper Plate and Shallow Subduction Megathrust Interface Over Seismic Cycles

The behavior of the shallow portion of the subduction zone, which generates the largest earthquakes and devastating tsunamis, is still insufficiently constrained. 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 frictional‐elastoplastic interaction between the megathrust interface and its overlying wedge causes variable surface strain signals such that the wedge strain patterns may reveal the mechanical state of the interface. To contribute to this understanding, we employ Seismotectonic Scale Modeling and simplify elastoplastic megathrust subduction to generate hundreds of analog seismic cycles at a laboratory scale and monitor the surface strain signals over the model's forearc across high to low temporal resolutions. We establish two compressional and critical wedge configurations to explore the mechanical and kinematic interaction between the shallow wedge and the interface. Our results demonstrate that this interaction can partition the wedge into different segments such that the anelastic extensional segment overlays the seismogenic zone at depth. Moreover, the different segments of the wedge may switch their state from compression/extension to extension/compression domains. We highlight that a more segmented upper plate represents megathrust subduction that generates more characteristic and periodic events. Additionally, the strain time series reveals that the strain state may remain quasi‐stable over a few seismic cycles in the coastal zone and then switch to the opposite mode. These observations are crucial for evaluating earthquake‐related morphotectonic markers and short‐term interseismic time series of the coastal regions

Natural Fractures Characterization and In Situ Stresses Inference in a Carbonate Reservoir—An Integrated Approach

In this paper, we characterized the natural fracture systems and inferred the state of in situ stress field through an integrated study in a very complex and heterogeneous fractured carbonate heavy oil reservoir. Relative magnitudes and orientations of the in-situ principal stresses in a naturally fractured carbonate heavy oil field were estimated with a combination of available data (World Stress Map, geological and geotectonic evidence, outcrop studies) and techniques (core analysis, borehole image logs and Side View Seismic Location). The estimates made here using various tools and data including routine core analysis and image logs are confirmatory to estimates made by theWorld Stress Map and geotectonic facts. NE-SW and NW-SE found to be the dominant orientations for maximum and minimum horizontal stresses in the study area. In addition, three dominant orientations were identified for vertical and sub-vertical fractures atop the crestal region of the anticlinal structure. Image logs found useful in recognition and delineation of natural fractures. The results implemented in a real field development and proved practical in optimal well placement, drilling and production practices. Such integrated studies can be instrumental in any E&P projects and related projects such as geological CO2 sequestration site characterization