Structure from Motion (SfM) generates high-resolution topography and coregistered texture (color) from an unstructured set of overlapping photographs taken from varying viewpoints, overcoming many of the cost, time, and logistical limitations of Light Detection and Ranging (LiDAR) and other topographic surveying methods. This paper provides the fi rst investigation of SfM as a tool for mapping fault zone topography in areas of sparse or low-lying vegetation. First, we present a simple, affordable SfM workfl ow, based on an unmanned helium balloon or motorized glider, an inexpensive camera, and semiautomated software. Second, we illustrate the system at two sites on southern California faults covered by existing airborne or terrestrial LiDAR, enabling a comparative assessment of SfM topography resolution and precision. At the fi rst site, an ~0.1 km 2 alluvial fan on the San Andreas fault, a colored point cloud of density mostly >700 points/m 2 and a 3 cm digital elevation model (DEM) and orthophoto were produced from 233 photos collected ~50 m above ground level. When a few global positioning system ground control points are incorporated, closest point vertical distances to the much sparser (~4 points/m 2) airborne LiDAR point cloud are mostly <3 cm. The second site spans an ~1 km section of the 1992 Landers earthquake scarp. A colored point cloud of density mostly >530 points/m 2 and a 2 cm DEM and orthophoto were produced from 450 photos taken from ~60 m above ground level. Closest point vertical distances to existing terrestrial LiDAR data of comparable density are mostly <6 cm. Each SfM survey took ~2 h to complete and several hours to generate the scene topography and texture. SfM greatly facilitates the imaging of subtle geomorphic offsets related to past earthquakes as well as rapid response mapping or long-term monitoring of faulted landscapes.

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Tsunamis are unpredictable and infrequent but potentially large impact natural disasters. To prepare, mitigate and prevent losses from tsunamis, probabilistic hazard and risk analysis methods have been developed and have proved useful. However, large gaps and uncertainties still exist and many steps in the assessment methods lack information, theoretical foundation, or commonly accepted methods. Moreover, applied methods have very different levels of maturity, from already advanced probabilistic tsunami hazard analysis for earthquake sources, to less mature probabilistic risk analysis. In this review we give an overview of the current state of probabilistic tsunami hazard and risk analysis. Identifying research gaps, we offer suggestions for future research directions. An extensive literature list allows for branching into diverse aspects of this scientific approach.

In December 2018, at the conclusion of its second implementation phase, the Global Earthquake Model (GEM) Foundation released its first version of a map outlining the spatial distribution of seismic hazard at a global scale. The map is the result of an extensive, joint effort combining the results obtained from a collection of probabilistic seismic hazard models, called the GEM Mosaic. Together, the map and the underlying database of models provide an up-to-date view of the earthquake threat globally. In addition, using the Mosaic, a synopsis of the current state-of-practice in modeling probabilistic seismic hazard at national and regional scales is possible. The process adopted for the compilation of the Mosaic adhered to the maximum extent possible to GEM’s principles of collaboration, inclusiveness, transparency, and reproducibility. For each region, priority was given to seismic hazard models either developed by well-recognized national agencies or by large collaborative projects involving local scientists. The version of the GEM Mosaic presented herein contains 30 probabilistic seismic hazard models, 14 of which represent national or sub-national models; the remainder are regional-scale models. We discuss the general qualities of these models, the underlying framework of the database, and the outlook for the Mosaic’s utility and its future versions.

Western Turkey has a long history of large earthquakes, but the responsible faults are poorly characterized. Here we reassess the past half century of instrumental earthquakes in the Simav‐Gediz region, starting with the 19 May 2011 Simav earthquake (Mw 5.9), which we image using interferometric synthetic aperture radar and regional and teleseismic waveforms. This event ruptured a steep, planar normal fault centered at 7–9 km depth but failed to break the surface. However, relocated main shock and aftershock hypocenters occurred beneath the main slip plane at 10–22 km depth, implying rupture initiation in areas of low coseismic slip. These calibrated modern earthquakes provide the impetus to relocate and reassess older instrumental events in the region. Aftershocks of the 1970 Gediz earthquake (Mw 7.1) form a narrow band, inconsistent with source models that invoke low‐angle detachment faulting, and may include events triggered dynamically by the unilateral main shock rupture. Epicenters of the 1969 Demirci earthquakes (Mw 5.9, 6.0) are more consistent with slip on the south dipping Akdağ fault than the larger, north dipping Simav fault. A counterintuitive aspect of recent seismicity across our study area is that the largest event (Mw 7.1) occurred in an area of slower extension and indistinct surface faulting, yet ruptured the surface, while recent earthquakes in the well‐defined and more rapidly extending Simav graben are smaller (Mw <6.0) and failed to produce surface breaks. Though our study area bounds a major metamorphic core complex, there is no evidence for involvement of low‐angle normal faulting in any of the recent large earthquakes.