Megathrust earthquakes along the South American subduction zone where the Nazca plate slips below the South American plate rapidly subducts below the South American plate contribute significantly to the seismic hazard in Chile, Peru, Ecuador and Colombia. Estimating recurrence of the megathrust events is of prime interest not only for securing effective counter measures for engineering purposes, but also for assessing seismic hazard and risk for appropriate disaster risk management solutions in the insurance sector. We present an evaluation and interpretation of recent research on the recurrence of megathrust earthquakes along the South America subduction zone. The modelling approach is conceptually founded in the asperity model and in this spirit evidence for documented earthquakes is assembled. We utilize time-independent and time-dependent recurrence models to understand the range and likelihood of recurrence times given the incomplete picture of the seismic history and the impact from uncertain event dates based on paleo-seismic / paleo-tsunami studies. In addition, we illustrate the sensitivity of recurrence rates for the largest earthquakes due to assumptions on seismic coupling and the size of potential ruptures. Downstream from the recurrence rate analysis, the results are used to estimate the impact of the subduction interface model seismicity on a select set of exposure subject to earthquake shaking due to those events. These examples highlight the potential range of seismic hazard and risk and set the basis to further constrain disaster risk management solutions.

A series of large subduction interface earthquakes along the South American coast caused large tsunamis in recent years. Each of these events, such as the 2010 Mw8.8 Maule and the 2015 Mw8.3 Illapel events, provided novel insights to improve tsunami hazard and risk modeling for the region, in particular due to the amount of data collected during post-seismic/ tsunami surveys reporting on coastal deformation, tsunami inundation, and building stock damage. These data are genuinely relevant to evaluate scenario modeling results supporting general approaches to model the tsunami hazard and risk. Despite the usefulness of rapidly determined finite-fault slip inversions for tsunami warning systems, the reliability of calculated elastic deformations along the coastline based on these models and subsequently tsunami flow depth and runup estimates might be questionable. We primarily shed light on the possible impact of using various solutions for selected historical events by performing full tsunami scenario calculation. We evaluate the inverted slip model solutions from the perspective of a tsunami modeler, i.e. we compare results of the elastic deformation modelling to observed coastal uplift and tsunami inundation against post-seismic survey data. These are important as coastal deformation strongly affects tsunami inundation results. Secondly, we compare observed data to modeled data from inverted slip distributions to solutions based on simulated slip distributions on the same fault geometries to understand the possible range of outcomes. . Given an inverted slip distribution, we first map those onto the Slab2.0 subduction interface and then calculate stochastic slip distributions. Thereafter, vertical seafloor/coastline deformations are computed using a triangular elastic dislocation model that captures the complexities of the subduction zone geometry. The deformations serve as initial conditions to a high-resolution numerical model that simulates the tsunami wave propagation and coastal inundations. Parallel computations are applied to overcome the large numerical computational efforts needed. Variable land surface roughness based on land cover data is used to simulate the accurate hydraulics of coastal inundation. Based on our modelling approach, we find that some published slip inversion models are deficient in modelling observed coastal deformation using an elastic deformation model. Only when including tsunami data for the inversions, these models tend to be better constrained. Without these data, finite fault slip inversions for local tsunami forecasts might be misleading in spatial inundation estimates as deformation results may be incorrect. This can happen both ways, either underestimating or overestimating tsunami inundations. While there are many additional aspects in the tsunami modelling procedure, this is an important basic aspect. Our results show that simulating stochastic slip distributions enables to cover the range of possible deformation and inundation results well. This result underlines that this approach is a useful tool to generate local probabilistic tsunami hazard and risk models.

Japan faces the world's highest tsunami hazard and risk due to its tectonic environment, high population density and exposure concentration along its coastlines. It is therefore of paramount interest to quantify and differentiate absolute and relative tsunami hazard and risk on a countrywide scale. We quantify tsunami hazard in terms of inundation depth for the entire Japanese coastline with a probabilistic tsunami hazard assessment utilizing the earthquake source information of the 2017 Japanese seismic hazard model. We simulate a stochastic event set for offshore earthquake sources and generate, for each single source with M-W >= 7.5, non-uniform finite-fault slip models. We calculate elastic seafloor and landmass deformations that serve as initial conditions to high resolution numerical modelling of tsunami wave propagation and coastal inundations by solving the nonlinear shallow water equation. Variable land surface roughness based on land cover data is used to simulate accurate hydraulics of coastal inundation. We differentiate tsunami hazard by inundation depth hazard curves and inundation depth return period maps aggregated to city ward polygons as meaningful administrative boundaries. We find mega-thrust events on the subduction interfaces constituting the largest hazard. However, events down to M-W >= 7.5 can contribute to substantial hazard in several regions along the coast. In particular for city wards within the Tokyo bay area, we find that earthquakes occurring on the Sagami trough and not the largest mega-thrust events on the Nankai trough, contribute to the highest inundation hazard. Our results also illustrate that tsunami hazard on the western Japanese coast is not negligible.

In this study we test whether principal components of the strain rate and stress tensors align within Switzerland. We find that 1) Helvetic Nappes line (HNL) is the relevant tectonic boundary to define different domains of crustal stress/surface strain rates orientations and 2) orientations of T- axes (of moment tensor solutions) and long-term asthenosphere cumulative finite strain (from SKS shear wave splitting) are consistent at the scale of the Alpine arc in Switzerland. At a more local scale, we find that seismic activity and surface deformation are in agreement but in three regions (Basel, Swiss Jura and Ticino); possibly because of the low levels of deformation and/or seismicity. In the Basel area, deep seismicity exists while surface deformation is absent. In the Ticino and the Swiss Jura, where seismic activity is close to absent, surface deformation is detected at a level of ~2 10 −8 /yr (~6.3 10 −16 /s).

The tsunami following the 2011 Tohoku megathrust earthquake of magnitude 9.0 showed the potential for significant damage and loss relevant to the insurance industry. To date, however, the perception of tsunami risk as compared to earthquake shaking risk remains limited in the insurance industry due to few available probabilistic tsunami risk models for the industry. Tsunami is considered a secondary peril to an earthquake model but requires large computational resources as it is a high-resolution peril as inundation and tsunami wave runup need to be calculated at high resolution. We therefore present the probabilistic tsunami model methodology that addresses these issues and is included in the 2018 RMS HD earthquake model for Japan. Based on the stochastic events of offshore earthquakes, we generate non-uniform finite fault slip models for events of MW≥7.5. Computed elastic seafloor/coastline deformations, peak slip and location of slip patches constrain the selection of slip models to match observations and expected variations. The deformations serve as initial conditions to the high-resolution numerical modeling of tsunami wave propagation and coastal inundations solving the non-linear shallow water equation. Variable land surface roughness based on land cover data is used to simulate accurate hydraulics of coastal inundation. Our results are based on the source geometries of the 2017 Japanese seismic hazard model. Inundation and tsunami runup results are compatible with measurements of the 2011 Tohoku earthquake and tsunami. The presented mean damage ratio patterns illustrate the high-resolution capabilities of the RMS tsunami model as basis for economic loss assessment.

Based on our experience in the project REAKT, we present a methodological framework to evaluate the potential benefits and costs of using earthquake early warning (EEW) and operational earthquake forecasting (OEF) for real-time mitigation of seismic risk at nuclear facilities. We focus on evaluating the reliability, significance and usefulness of the aforementioned real-time risk-mitigation tools and on the communication of real-time earthquake information to end-users. We find that EEW and OEF have significant potential for the reduction of seismic risk at nuclear plants, although much scientific research and testing is still necessary to optimise their operation for these sensitive and highly-regulated facilities. While our test bed was Switzerland, the methodology presented here is of general interest to the community of EEW researchers and end-users and its scope is significantly beyond its specific application within REAKT.

A likely source of earthquake clustering is static stress transfer between individual events. Previous attempts to quantify the role of static stress for earthquake triggering generally considered only the stress changes caused by large events, and often discarded data uncertainties. We conducted a robust two-fold empirical test of the static stress change hypothesis by accounting for all events of magnitude M>=2.5 and their location and focal mechanism uncertainties provided by catalogs for Southern California between 1981 and 2010, first after resolving the focal plane ambiguity and second after randomly choosing one of the two nodal planes. For both cases, we find compelling evidence supporting the static triggering with stronger evidence after resolving the focal plane ambiguity above significantly small (about 10 Pa) but consistently observed stress thresholds. The evidence for the static triggering hypothesis is robust with respect to the choice of the friction coefficient, Skempton's coefficient and magnitude threshold. Weak correlations between the Coulomb Index (fraction of earthquakes that received positive Coulomb stress change) and the coefficient of friction indicate that the role of normal stress in triggering is rather limited. Last but not the least, we determined that the characteristic time for the loss of the stress change memory of a single event is nearly independent of the amplitude of the Coulomb stress change and varies between 95 and 180 days implying that forecasts based on static stress changes will have poor predictive skills beyond times that are larger than a few hundred days on average.

AbstractWe combine temporal variability in local seismic activity rates and size distributions to estimate the evolution of a Gutenberg‐Richter‐based metric, the normalized rupture potential (NRP), comparing differences between smaller and larger earthquakes. For the Pacific Plate off Japan, we study both complex spatial patterns and how they evolve over the last 18 years, and more detailed temporal characteristics in a simplified spatial selection, i.e., inside and outside the high‐slip zone of the 2011 M9 Tohoku earthquake. We resolve significant changes, in particular an immediate NRP increase for large events prior to the Tohoku event in the subsequent high‐slip patch, a very rapid decrease inside this high‐stress‐release area coupled with a lasting increase of NRP in the immediate surroundings. Even in the center of the Tohoku rupture, the NRP for large magnitudes has not dropped below the 12 year average and is not significantly different from conditions a decade before the M9 event.

The last decade has shown the social and economic vulnerability of countries in South-East Asia to earthquake hazard and risk. The 2004 M9.2 Sumatra earthquake and the associated tsunami caused significant casualties and economic losses generating major attention internationally due to the scale of its impact across the urban areas of South-East Asia and Indian Ocean (Indonesia, Thailand, Sri Lanka, and India). While many disaster mitigation programs to improve societal earthquake resilience are under way focusing on saving lives and livelihoods, the risk management sector is challenged to model economic consequences. We present the hazard component suitable for a South-East Asia earthquake risk model covering Indonesia, Malaysia, Singapore, Thailand, Vietnam and the Philippines. The consistent regional model builds upon refined modelling approaches for 1) background seismicity, i.e. earthquakes not occurring on mapped fault structures, 2) seismic activity from geologic and geodetic data on crustal faults and 3) along the interface of subduction zones. We elaborate on building rate model for crustal fault systems (e.g. Sumatra fault zone, Philippine fault zone) as well as the subduction zones and showcase its characteristics. We combine this with an up-to-date ground motion model that is suitable for this tectonically complex area. We assign more weights to globally developed ground motion prediction equations (GMPEs) due to the scarcity of strong ground motion data in Southeast Asia. We analyze the components of the risk model per country by computing the contributions by source type to typical risk metrics (return period losses, average annual loss) and considering the impact of the hazard model on all lines of business.

We examine interseismic coupling of the Manila subduction zone and fault activity in the Luzon area using a block model constrained by GPS data collected from 1998 to 2015. Estimated long‐term slip rates along the Manila subduction zone show a gradual southward decrease from 90–100 mm/yr at the northwest tip of Luzon to 65–80 mm/yr at the southern portion of the Manila Trench. We provide two block models (models A and B) to illustrate possible realizations of coupling along the Manila Trench, which may be used to infer future earthquake rupture scenarios. Model A shows a low coupling ratio of 0.34 offshore western Luzon and continuous creeping on the plate interface at latitudes 18–19°N. Model B includes the North Luzon Trough Fault and shows prevalent coupling on the plate interface with a coupling ratio of 0.48. Both models fit GPS velocities well, although they have significantly different tectonic implications. The accumulated strain along the Manila subduction zone at latitudes 15–19°N could be balanced by earthquakes with composite magnitudes of Mw 8.8–9.2, assuming recurrence intervals of 500–1000 years. GPS observations are consistent with full locking of the majority of active faults in Luzon to a depth of 20 km. Inferred moments of large inland earthquakes in Luzon fall in the range of Mw 6.9–7.6 assuming a recurrence interval of 100 years.

The 2011 Tohoku megathrust earthquake of magnitude 9.0 (MW) showed the potential of significant loss to insurance industry due to tsunami. Large magnitude earthquakes at the Cascadia Subduction Zone (CSZ) can cause the most devastating tsunami hazard in the pacific basin to the west coast of USA including Washington, Oregon, and north California coastlines. The perception of tsunami risk in the industry has been small compared to the risk from the shake damage. To improve managing the tsunami risk for USA coastal cities, Risk management Solution (RMS) first modeled the historical 1700 Cascadia tsunami event and evaluated the maximum tsunami waves at different stations offshore of west coast of USA as well as coastal inundation. Then we developed a set of stochastic slip distributions along the CSZ corresponding to the large earthquakes with moment magnitude (MW) higher than 8.0 and modeled the tsunami wave propagation and coastal inundation. Each tsunami event is built based on seismic characteristics of the CSZ ruptures and a slip model that provides a non-uniform slip distribution. Non-uniform slip distributions are used to provide a realistic set of possible tsunami generating earthquakes and are constrained by the paleo-seismic records of offshore uplifts along west of USA. The vertical seafloor/coastline deformations including uplift and subsidence are computed using a triangular dislocation model that captures the complexities of the subduction zone geometry. These deformations are then used as initial conditions to a high-resolution numerical model that simulates the tsunami wave propagation and coastal inundations. Parallel computations are applied on Graphic Processing Units (GPUs) to overcome the large numerical computational efforts needed to model the entire west coast of USA. Variable land surface roughness based on land cover data is used to simulate the accurate hydraulics of coastal inundation. The tsunami hazard maps are developed for the entire west coast of USA starting from Washington state coast at north to California state coasts in south. In addition the histograms of maximum tsunami waves for key coastal cities are provided. This paper mainly covers the hazard aspect of tsunami evaluation and simulation for west coast of USA. In parallel RMS has developed an extensive study on the vulnerability of infrastructures and buildings along west of USA as well as the detailed information of exposure. The hazard model will later be combined with the vulnerability model and exposure model to provide a comprehensive understanding of tsunami risk and economic loss along the west coast of USA due to megathrust earthquakes in CSZ.

One of the major unresolved questions in Seismology is the evolution in time and space of the earthquake rupture potential and thus time-dependent hazard along active faults. What happens after a major event: is the potential for further large events reduced as predicted from elastic rebound, or increased as proposed by current-state short-term clustering models? How does the rupture potential distribute in space, i.e. does it reveal imprints of stress transfer? Based on the rich earthquake record along the Pacific Plate off Japan we investigate what information on spatial distributions and temporal changes of normalized rupture potential (NRP) for different magnitudes can be derived from time-varying, local statistical characteristics of well and frequently observed small-to-moderate seismicity. The NRP is obtained from the frequency-magnitude distribution of sampled earthquakes, specifically from the slope (b-value) and y-intercept (a-value) of this distribution, in a log-linear plot. The b-values describe the relative frequency of large versus small earthquakes, while a-values express the seismic activity during the observation period (in this study, the a-values are annualized and distance-weighted, i.e. we consider the relative earthquake-grid-point distances, with close-by events gaining higher weights than more distant events). We analyze the seismicity from 1998 ~ 2015, including the massive 2011 M9 Tohoku-oki earthquake and its aftermath. Seismicity records show strong spatio-temporal variability in both activity rates and size distribution. We show first (Tormann et al., 2015) that the size distribution of earthquakes has significantly changed before (increased fraction of larger magnitudes –relatively small b-values) and after that mainshock (increased fraction of smaller magnitudes –relatively large b-values); these changes are particularly stronger in areas of highest Tohoku-oki coseismic

The last decade has shown the social and economic vulnerability of countries in South-East Asia to earthquake hazard and risk. While many disaster mitigation programs to improve societal earthquake resilience are under way focusing on saving lives and livelihoods, the risk management sector is challenged to model economic consequences. We present the hazard component suitable for a South-East Asia earthquake risk model covering Indonesia, Malaysia, the Philippines and Indochine countries. The consistent regional model builds upon refined modelling approaches for 1) background seismicity, i.e. earthquakes not occurring on mapped fault structures, 2) seismic activity from geologic and geodetic data on crustal faults and 3) along the interface of subduction zones. We elaborate on building a self-consistent rate model for crustal fault systems (e.g. Sumatra fault zone, Philippine fault zone) as well as the subduction zone, showcase its characteristics and combine this with an up-to-date ground motion model. We aim to present insights on the impact of the different hazard components on the final risk model.

We present the "condensation" method that exploits the heterogeneity of the probability distribution functions (PDFs) of event locations to improve the spatial information content of seismic catalogs. As its name indicates, the condensation method reduces the size of seismic catalogs while improving the access to the spatial information content of seismic catalogs. The PDFs of events are first ranked by decreasing location errors and then successively condensed onto better located and lower variance event PDFs. The obtained condensed catalog differs from the initial catalog by attributing different weights to each event, the set of weights providing an optimal spatial representation with respect to the spatially varying location capability of the seismic network. Synthetic tests on fractal distributions perturbed with realistic location errors show that condensation improves spatial information content of the original catalog, which is quantified by the likelihood gain per event. Applied to Southern California seismicity, the new condensed catalog highlights major mapped fault traces and reveals possible additional structures while reducing the catalog length by ∼25%. The condensation method allows us to account for location error information within a point based spatial analysis. We demonstrate this by comparing the multifractal properties of the condensed catalog locations with those of the original catalog. We evidence different spatial scaling regimes characterized by distinct multifractal spectra and separated by transition scales. We interpret the upper scale as to agree with the thickness of the brittle crust, while the lower scale (2.5 km) might depend on the relocation procedure. Accounting for these new results, the epidemic type aftershock model formulation suggests that, contrary to previous studies, large earthquakes dominate the earthquake triggering process. This implies that the limited capability of detecting small magnitude events cannot be used to argue that earthquakes are unpredictable in general.

The 2013 European Seismic Hazard Model (ESHM13) results from a community-based probabilistic seismic hazard assessment supported by the EU-FP7 project “Seismic Hazard Harmonization in Europe” (SHARE, 2009–2013). The ESHM13 is a consistent seismic hazard model for Europe and Turkey which overcomes the limitation of national borders and includes a through quantification of the uncertainties. It is the first completed regional effort contributing to the “Global Earthquake Model” initiative. It might serve as a reference model for various applications, from earthquake preparedness to earthquake risk mitigation strategies, including the update of the European seismic regulations for building design (Eurocode 8), and thus it is useful for future safety assessment and improvement of private and public buildings. Although its results constitute a reference for Europe, they do not replace the existing national design regulations that are in place for seismic design and construction of buildings. The ESHM13 represents a significant improvement compared to previous efforts as it is based on (1) the compilation of updated and harmonised versions of the databases required for probabilistic seismic hazard assessment, (2) the adoption of standard procedures and robust methods, especially for expert elicitation and consensus building among hundreds of European experts, (3) the multi-disciplinary input from all branches of earthquake science and engineering, (4) the direct involvement of the CEN/TC250/SC8 committee in defining output specifications relevant for Eurocode 8 and (5) the accounting for epistemic uncertainties of model components and hazard results. Furthermore, enormous effort was devoted to transparently document and ensure open availability of all data, results and methods through the European Facility for Earthquake Hazard and Risk (www.efehr.org).

Constraints on the recurrence times of subduction zone earthquakes are important for seismic hazard assessment and mitigation. Models of such megathrust earthquakes often assume that subduction zones are segmented and earthquakes occur quasi-periodically owing to constant tectonic loading. Here we analyse the occurrence of small earthquakes compared to larger ones-the b-values-on a 1,000-km-long section of the subducting Pacific Plate beneath central and northern Japan since 1998. We find that the b-values vary spatially and mirror the tectonic regime. For example, high b-values, indicative of low stress, occur in locations characterized by deep magma chambers and low b-values, or high stress, occur where the subducting and overriding plates are strongly coupled. There is no significant variation in the low b-values to suggest the plate interface is segmented in a way that might limit potential ruptures. Parts of the plate interface that ruptured during the 2011 Tohoku-oki earthquake were highly stressed in the years leading up to the earthquake. Although the stress was largely released during the 2011 rupture, we find that the stress levels quickly recovered to pre-quake levels within just a few years. We conclude that large earthquakes may not have a characteristic location, size or recurrence interval, and might therefore occur more randomly distributed in time.