Fault slip and earthquake recurrence along strike-slip faults - Contributions of high-resolution geomorphic data

International audienceUnderstanding earthquake (EQ) recurrence relies on information about the timing and size of past EQ ruptures along a given fault. Knowledge of a fault's rupture history provides valuable information on its potential future behavior, enabling seismic hazard estimates and loss mitigation. Stratigraphic and geomorphic evidence of faulting is used to constrain the recurrence of surface rupturing EQs. Analysis of the latter data sets culminated during the mid-1980s in the formulation of now classical EQ recurrence models, now routinely used to assess seismic hazard. Within the last decade, Light Detection and Ranging (lidar) surveying technology and other high-resolution data sets became increasingly available to tectono-geomorphic studies, promising to contribute to better-informed models of EQ recurrence and slip-accumulation patterns. After reviewing motivation and background, we outline requirements to successfully reconstruct a fault's offset accumulation pattern from geomorphic evidence. We address sources of uncertainty affecting offset measurement and advocate approaches to minimize them. A number of recent studies focus on single-EQ slip distributions and along-fault slip accumulation patterns. We put them in context with paleoseismic studies along the respective faults by comparing coefficients of variation CV for EQ inter-event time and slip-per-event and find that a) single-event offsets vary over a wide range of length-scales and the sources for offset variability differ with length-scale, b) at fault-segment length-scales, single-event offsets are essentially constant, c) along-fault offset accumulation as resolved in the geomorphic record is dominated by essentially same-size, large offset increments, and d) there is generally no one-to-one correlation between the offset accumulation pattern constrained in the geomorphic record and EQ occurrence as identified in the stratigraphic record, revealing the higher resolution and preservation potential of the latter. While slip accumulation along a fault segment may be dominated by repetition of large, nearly constant offset increments, timing of surface-rupture is less regular

Very High Resolution Photogrammetric DSMs and True-Orthoimages: 3D-Fault Zone Mapping in Northern Chile

Both Digital Surface Models (DSM) and aerial imagery are commonly used to map and assess geologic structures from remote sensing data. Here we present a high-resolution topographic and visual data set from the Atacama fault system (AFS) near Antofagasta, Chile. The data were acquired with the Modular Airborne Camera System – MACS – (Lehmann et al. 2011) developed by the DLR (German Aerospace Center) in Berlin, Germany. Photogrammetric processing including dense image matching with SGM (Hirschmueller, 2008) and orthorectification was conducted using the processing chain at DLR. The data show a very high geometric accuracy which is the basis for multitemporal analysis. The DSM and the co-registered True Ortho Images with 5cm ground resolution permit the identi­cation of very small-scale geomorphic features. The data used are part of an ongoing study on the geologic history of the AFS in Northern Chile in the context of earthquake prediction. A primary step towards assessing time and size of future earthquakes is the identi­cation of earthquake recurrence patterns in the existing seismic record. Geologic and geomorphic data are commonly analyzed for this purpose, reasoned by the lack of sufficiently long historical or instrumental seismic data sets. Until recently, those geomorphic data sets encompassed field observation, local total station surveys, and aerial photography. Over the last decade, LiDAR-based high-resolution topographic data sets (e.g. Zielke et al. 2010) became an additional powerful mean, contributing distinctly to a better understanding of earthquake rupture characteristics (e.g., single-event along-fault slip distribution, along-fault slip accumulation pattern) and their relation to fault geometric complexities. Compared to typical LiDAR-DEM (with ~0.5m grid size), ground resolution of the MACS-DSM is increased by an order of magnitude while the spatial extend of these data set is essentially the same. We present examples of the 5cm resolution data set and further explore resolution capabilities and potential with regards to the aforementioned tectono-geomorphic questions

Resolving Quaternary Tectonic Activity with High-Resolution Data in Space and Time

AbstractLarge earthquakes are among the most dangerous natural disasters with potentially devastating effects on society and infrastructure across the globe. In order to better understand earthquakes, research in active tectonics aims at quantifying crustal deformation throughout the active fault’s earthquake cycles by studying geomorphic and stratigraphic evidence of recent and past earthquakes. The underlying assumption in this approach is that a fault’s current and previous seismic behavior is representative of its future behavior. Constraining a fault’s seismic behavior in such a manner requires high-resolution geomorphic and stratigraphic records that enable us to resolve the spatial and temporal characteristics of co-, post-, and interseismic phases, ideally over multiple earthquake cycles. Recent technological developments have dramatically increased not only the amount and resolution of topographic and geophysical survey data sets but also our ability to date stratigraphic units and geomorphic surfaces. These technological advances have enabled us to better understand the interplay between crustal deformation, earthquake ruptures, and their signature in geomorphic and stratigraphic records. In particular, the availability of high-resolution data sets from LiDAR, SfM, or geophysical surveys and the use of accurate dating methods such as cosmogenic or OSL dating allow us to quantitatively study surface deformation at high spatial resolution over large areas and at multiple time scales—from a few years to millions of years. In this special issue, we focus on the tectonic activity of active faults and the geomorphic processes in various tectonic regimes worldwide. It covers active tectonics, earthquake geology, remote sensing, tectonic geomorphology, Quaternary geochronology, geohazard, and seismology

Bedrock fault roughness resolves slip increments of large earthquakes: Case studies from Central Italy

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The First Network of Ocean Bottom Seismometers in the Red Sea to Investigate the Zabargad Fracture Zone

In the last decades, the slow-spreading Red Sea rift has been the objective of several geophysical investigations to study the extension of the oceanic crust, the thickness of the sedimentary cover, and the formation of transform faults. However, local seismology datasets are still lacking despite their potential to contribute to the understanding of the tectonic evolution of the Red Sea. The Zabargad Fracture Zone is located in the Northern Red Sea and significantly offsets the rift axis to the East. Thus, it is considered a key tectonic element to understand better the formation of the Red Sea rift. To fill the gap in the dataset availability, we deployed the first passive seismic network in the Red Sea, within the Zabargad Fracture Zone. This network included 12 Lobster OBSs from the DEPAS pool, 2 OBS developed and deployed by Fugro, and 4 portable seismic land stations deployed on islands and onshore on the Saudi Arabian coast. Our data-quality analysis confirms that the head-buoy cable free to strum, as well as other additional elements of the DEPAS OBSs, generate seismic noise at frequencies $>$ 10 Hz. However, the Fugro OBSs show high-frequency disturbances even if they lack vibrating elements. Comparison between land and OBS stations reveals that noise between 1 and 10 Hz is due to ocean-generated seismic noise, and not due to resonance of the OBS elements. We also found that waveforms of teleseismic earthquakes recorded by the Fugro OBSs, islands, and onshore stations have comparable signal-to-noise ratios. Instead, differences in signal-to-noise ratio for local earthquakes are affected more by site and path effects than instrument settings