京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18081号 / 理博第3959号 / 新制||理||1571(附属図書館) / 30939 / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)准教授 宮﨑 真一, 教授 福田 洋一, 教授 平原 和朗 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

I use Synthetic Aperture Radar Interferometry (InSAR) to study the present deformation in the Western Basin and Range and Basin and Range - Sierra Nevada transition. I process 350 SAR data over 190·103 km2 for the period 1992 to 2002. Both stacking and time series processing were applied to produce precise (mm/yr) and high-resolution velocity map for the area. Two new processing techniques have been developed. The first technique solves for the long wavelength ambiguities of the InSAR derived velocity map that arise due to uncertainty in the orbital parameter of the satellite. The technique assimilates continuous GPS data into the InSAR time-series processing. The second technique extracts the horizontal and vertical components of the deformation field from two adjacent radar tracks. I applied stacking to study the transient deformation across the Central Nevada Seismic Belt and interseismic strain accumulation across the Eastern California Shear Zone. I show that the current deformation across the Central Nevada Seismic Belt can be explained by a combination of inter-seismic, post-seismic and anthropogenic deformation. The Post-Seismic deformation is associated with visco-elastic relaxation of the Earth's mantle in response to a centennial earthquake sequence of five ~M7 earthquakes along the Central Nevada Seismic Belt. The anthropogenic deformation is a response of the bedrock to water withdrawal in support of mining activity. A more evolved time-series approach that solves for orbital errors is applied across the Eastern California Shear Zone. The study shows that the Hunter Mountain - Panamint Valley fault system accommodates ~5 mm/yr, a faster rate than geological averages. The region of strain accumulation is a narrow band of ~10 km centered on the Hunter mountain fault, and indicates a very shallow locking depth in agreement with an active low angle normal fault system.

abstract: Meter-resolution topography gathered by LiDAR (Light Detection and Ranging) has become an indispensable tool for better understanding of many surface processes including those sculpting landscapes that record information about earthquake hazards for example. For this reason, and because of the spectacular representation of the phenomena that these data provide, it is appropriate to integrate these data into Earth science educational materials. I seek to answer the following research question: "will using the LiDAR topography data instead of, or alongside, traditional visualizations and teaching methods enhance a student's ability to understand geologic concepts such as plate tectonics, the earthquake cycle, strike-slip faults, and geomorphology?" In order to answer this question, a ten-minute introductory video on LiDAR and its uses for the study of earthquakes entitled "LiDAR: Illuminating Earthquake Hazards" was produced. Additionally, LiDAR topography was integrated into the development of an undergraduate-level educational activity, the San Andreas fault (SAF) earthquake cycle activity, designed to teach introductory Earth science students about the earthquake cycle. Both the LiDAR video and the SAF activity were tested in undergraduate classrooms in order to determine their effectiveness. A pretest and posttest were administered to introductory geology lab students. The results of these tests show a notable increase in understanding LiDAR topography and its uses for studying earthquakes from pretest to posttest after watching the video on LiDAR, and a notable increase in understanding the earthquake cycle from pretest to posttest using the San Andreas Fault earthquake cycle exercise. These results suggest that the use of LiDAR topography within these educational tools is beneficial for students when learning about the earthquake cycle and earthquake hazards. / Dissertation/Thesis / M.S. Geological Sciences 2011

Localized geodetic deformation of an approximately arctangent shape around locked strike-slip faults is widely reported, but there are also important exceptions showing distributed interseismic deformation. Understanding the controlling mechanism is important to the interpretation of geodetic observations for hazard assessment and geodynamic analysis. In this thesis, I use simple finite element models to separately study the two major contributors to the deformation: far-field loading and previous earthquakes. The models feature a vertical strike-slip fault in an elastic layer overlying a viscoelastic substrate of Maxwell or Burgers rheology, with or without weaknesses representing extensions of the fault either along strike or to greater depth. If the locked fault is loaded only from the far field without the effects of previous earthquakes, localized deformation occurs only if local mechanical weaknesses below the fault and/or somewhere along strike are introduced. I first show that the effects of far-field loading are rather limited even in the presence of extreme weaknesses. Then I use idealized earthquake cycle models to investigate the effects of past seismic events in a viscoelastic Earth. I demonstrate that, after a phase of fast postseismic deformation just after the earthquake, the localization of interseismic deformation is controlled mainly by the recurrence interval of past earthquakes. Given viscosity, shorter recurrence leads to greater interseismic localization, regardless of the rheological model used. The presence of a low-viscosity deep fault zone does not change this conclusion, although it tends to lessen localization by promoting faster postseismic stress relaxation. Distributed interseismic deformation, although less reported in the literature, is a natural consequence of very long recurrence and in theory should be as common as localized deformation. The apparent propensity of the latter is likely associated with the much greater quantity and better quality of geodetic observations from higher-rate and shorter-recurrence faults. Using viscoelastic earthquake-cycle models, I also explore the role of nearby earthquakes and creeping segments along the same fault. For faults of relatively short recurrence, frequent ruptures of nearby segments, modelled using a migrating rupture sequence with or without temporal clustering, further enhance localization. For faults of very long recurrence, faster near-fault deformation induced by a recent earthquake may give a false impression of localized interseismic deformation. / Graduate

La zone de subduction entre les plaques Nazca et Amérique du Sud est une des régions les plus actives de notre planète. De grands tremblements de terre et tsunamis associés se produisent de façon récurrente presque tout au long de sa marge. Néanmoins, le segment de subduction au nord du Pérou (de lat.3oS à 9oS) est resté le seul segment sismiquement silencieux depuis les premières informations historiques sur les séismes qui remontent au XVème siècle. Avant les travaux présentés dans ce manuscrit, aucune information sur les processus accommodant la convergence de la plaque Nazca vers le continent Sud-Américain n’était disponible le long du segment de 1000km au nord Pérou et sud Equateur. Les techniques de géodésie spatiale, en particulier le GPS/GNSS, nous permettent de quantifier les mouvements à la surface de la plaque supérieure avec une précision millimétrique. Ces mesures, couplées à l'utilisation de modèles élastiques, nous permettent de déterminer le niveau du couplage intersismique le long de l'interface entre les plaques. Le but de ma thèse est d'étudier le cycle sismique et la déformation continentale le long de la zone de subduction du Pérou, avec un intérêt particulier pour son segment nord. Nous utilisons des mesures GPS acquises depuis 2008 dans le cadre d'un projet international (le projet Andes Du Nord, ANR- ADN). Le champ de vitesse GPS obtenu couvre l’ensemble de la marge de subduction péruvienne, avec des mesures dans la cordillère et dans une moindre mesure dans la région sub-Andine. L'analyse et la modélisation du champ de vitesse GPS ont permis d'obtenir les résultats suivants: Premièrement: nous mettons en évidence l'existence d'un nouveau domaine continental, que nous avons baptisé comme le sliver Inca et qui est en translation a une vitesse de 4-5 mm/an en direction sud-est par rapport au craton Sud Américain. Le sliver Inca s’étend tout le long de la marge péruvienne. / The Nazca/South American subduction zone is one of the most active regions on Earth. Large earthquakes and associated tsunamis occur recurrently almost all along its margin. Nevertheless, the ~1000 km long (from lat.2oS to 9oS) segment in northern Peru and southern Ecuador subduction has remained in relative seismic silence for at least the past five centuries. Before the work presented in this thesis, no information about the processes accommodating the convergence was available for this region and it was impossible to answer whether it could host a great Mw>8.5 earthquake in future or not. Nowadays, spatial geodesy, and more specifically GPS/GNSS enable us to quantify the surface displacement on the overriding plate with millimeter accuracy. Geodetic measurements together with the use of elastic models allow us to determine the amount of interseismic coupling at the plate interface. My thesis focuses on the seismic cycle and the continental deformation along the Peruvian subduction margin, with particular interest along its northern and central segments. We use GPS measurements acquired since 2008 in the frame of an international French-Peruvian- Ecuadorian project (the Andes Du Nord project, ADN). Our GPS velocity field covers the entire Peruvian subduction margin, with measurements in the Andean cordillera and part of the sub-Andean region. Modeling of GPS velocity field show the existence of a new tectonic microplate that we baptized as the Inca Sliver, which is in southeastward translation a rate of 4-5 mm/yr with respect to stable South America.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22256号 / 理博第4570号 / 新制||理||1656(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)准教授 西村 卓也, 教授 福田 洋一, 准教授 深畑 幸俊 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18800号 / 理博第4058号 / 新制||理||1584(附属図書館) / 31751 / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 平原 和朗, 教授 澁谷 拓郎, 准教授 久家 慶子 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

The slip behaviour of subduction faults and the viscoelastic rheology of Earth’s mantle govern crustal deformation throughout the subduction earthquake cycle. This Ph.D. dissertation presents research results on two topics: (1) coseismic and postseismic slip of the shallowest segment of subduction faults and (2) postseismic deformation following great subduction earthquakes controlled by mantle viscoelasticity. Topic 1: Slip behaviour of the shallowest subduction faults. By modelling high-resolution cross-trench bathymetry surveys before and after the 2011 Mw 9.0 Tohoku-oki earthquake, we determine the magnitude and distribution of coseismic slip over the most near-trench 40 km of the Japan Trench megathrust. The inferred > 60 m average slip and a gentle increase by 5 m towards the trench over this distance indicate moderate degree of net coseismic weakening of the shallow fault. Using near-trench seafloor and sub-seafloor fluid pressure variations as strain indicators in conjunction with land-based geodetic measurements, we determine coseismic-slip and afterslip distributions of the 2012 Mw 7.6 Costa Rica earthquake. Here, trench-breaching slip similar to the Tohoku-oki rupture did not occur during the earthquake, but afterslip extended to the trench axis and reached ~0.7 m over 1.3 years after the earthquake, exhibiting a velocity-strengthening behaviour. These two contrasting examples bracket a possibly wide range of slip behaviour of the shallow megathrust. They help us understand why large tsunamis are generated by some but not all subduction earthquakes. Topic 2: Postseismic deformation following great subduction earthquakes. Due to the asymmetry of megathrust rupture, with the upper plate undergoing greater coseismic tension than the incoming plate, viscoelastic stress relaxation causes the trench and land areas to move in opposite, opposing directions immediately after the earthquake. Seafloor geodetic measurements following the 2011 Tohoku-oki earthquake, modelled in this work, provided the first direct observational evidence for this effect. Systematic modelling studies in this work suggest that such viscoelastic opposing motion should be common to all Mw ≥ 8 subduction earthquakes. As the effect of viscoelastic relaxation decays with time and the effect of fault relocking becomes increasingly dominant, the dividing boundary of the opposing motion continues to migrate away from the rupture area. Comparative studies of ten 8 ≤ Mw ≤ 9.5 subduction earthquakes in this dissertation quantifies the primary role of earthquake size in controlling the “speed” of the evolution of this deformation. Larger earthquakes are followed by longer-lived opposing motion that affects a broader region of the upper plate. / Graduate