OpenQuake Engine Research Articles

FaultQuake: An open-source Python tool for estimating Seismic Activity Rates in faults

In regions experiencing ongoing aseismic deformation, fault’s Activity Rate (AR) calculations often lead to an overestimation of hazard potential. This study proposes a novel methodology that integrates the Seismic Coupling Coefficient (SCC) into the fault Seismic Activity Rate (SAR) calculation process to discriminate seismic moment rates. We introduce FaultQuake, an open-source Python tool equipped with a Graphical User Interface (GUI), designed to implement this methodology and accurately estimate SAR for faults. These activity rates can be included in Probabilistic Seismic Hazard Assessment (PSHA) frameworks and assist in differentiating the seismic and aseismic deformation. FaultQuake also presents an innovative embedded workflow, the Optimal Value Computation Workflow (OVCW), based on Conflation of Probabilities (CoP), for calculating the Maximum Magnitude (Mmax) from the empirical relationships and the observed magnitudes (Mobs) assigned to a single fault. This enhancement improves the estimation of seismic moment rates and the SAR calculation process. FaultQuake outputs are provided in the format of OpenQuake engine input files to facilitate the PSHA process. We present a sample case study focusing on the PSHA of a region in southern Iran characterized by a substantial aseismic deformation to illustrate the practical application of FaultQuake in seismic hazard analysis. Peak Ground Acceleration (PGA) maps for 10% and 2% Probabilities of Exceedance (PoE) are plotted to compare PGAs with and without applying the FaultQuake algorithm. The results provide an enhanced view of the area’s hazard with mitigation of the overestimation, resulting in more representative hazard maps. The source codes of FaultQuake are available at the FaultQuake GitHub repository, contributing to the computer and geoscience community.

Seismic Risk Model for the Beijing–Tianjin–Hebei Region, China: Considering Epistemic Uncertainty from the Seismic Hazard Models

This study presents a probabilistic seismic risk model for the Beijing–Tianjin–Hebei region in China. The model comprises a township-level residential building exposure model, a vulnerability model derived from the Chinese building taxonomy, and a regional probabilistic seismic hazard model. The three components are integrated by a stochastic event-based method of the OpenQuake engine to assess the regional seismic risk in terms of average annual loss and exceedance probability curve at the city, province, and regional levels. The novelty and uniqueness of this study are that a probabilistic seismic risk model for the Beijing–Tianjin–Hebei region in China is developed by considering the impact of site conditions and epistemic uncertainty from the seismic hazard model.

Large-scale damage assessment of buildings considering SSI and site amplification: The case of Thessaloniki

Our study introduces a methodology to improve large-scale seismic damage assessment by incorporating site-specific fragility curves, considering soil–structure interaction (SSI) and site amplification (SAmp) effects. The proposed method proposes an enhanced building exposure model, using publicly available data and the open-source OpenQuake Engine software. The objective is to determine whether a more refined approach incorporating SSI and SAmp can impact the final damage calculation. We evaluate our approach by estimating the damage distribution for the Thessaloniki 1978 earthquake scenario using the actual building stock of Thessaloniki. We present several maps with aggregated damages at different levels to investigate the spatial variability of SSI and SAmp, and their influence on the resulting damages. Our estimated physical damages have been compared with those obtained using approaches from the existing literature. Apparently, using an updated building exposure model to assess damages makes any comparison with past observed damages challenging. Nevertheless, incorporating SSI and SAmp in large-scale damage assessment can provide valuable support for strategic decision-making in cities and improve the accuracy of the expected loss assessment due to a seismic event.

The seismic hazard from the Lembang Fault, Indonesia, derived from InSAR and GNSS data

Abstract. A growing number of large cities are located near poorly understood faults that have not generated a significant earthquake in recent history. The Lembang Fault is one such fault located near the city of Bandung in West Java, Indonesia. The slip rate on this fault is debated, with estimates ranging from 6 to 1.95–3.45 mm yr−1, derived from a GNSS (global navigation satellite system) campaign and geological measurements respectively. In this paper we measure the surface deformation across the Bandung region and resolve the slip rate across the Lembang Fault using radar interferometry (InSAR – interferometric synthetic aperture radar) analysis of 6 years of Sentinel-1 satellite data and continuous GNSS measurements across the fault. Our slip rate estimate for the fault is 4.7 mm yr−1, with the shallow portions of the fault creeping at 2.2 mm yr−1. Previous studies estimated the return period of large earthquakes on the fault to be between 170–670 years. Assuming simplified fault geometries and a reasonable estimate of the seismogenic depth we derive an estimated moment deficit equivalent to magnitude 6.6–7.0 earthquakes, indicating that the fault poses a very real hazard to the local population. Using the Global Earthquake Model OpenQuake engine we calculate ground motions for these two earthquake scenarios and estimate that 1.9–2.7 million people within the Bandung metropolitan region would be exposed to ground shaking greater than 0.3 g. This study highlights the importance of identifying active faults, understanding their past activity, and measuring the current strain rates of smaller crustal active faults located near large cities in seismic zones.

Probabilistic seismic hazard and risk assessment of Mizoram, North East India

This paper presents seismic hazard and risk assessment for the state of Mizoram based on a classical probabilistic seismic hazard analysis and event-based probabilistic seismic risk analysis. For the seismic hazard estimation, analysis has been performed considering the areal source model, fault zone polygon, and smoothed gridded seismicity model. The earthquake activity rates for these source zones and smoothed gridded seismicity sources are estimated from the homogenized and declustered earthquake catalogue. The logic tree framework is applied in the seismic source models and Ground Motion Prediction equations (GMPEs) to account for the epistemic uncertainties. Five Next-generation attenuation (NGA) GMPEs for the active shallow region and three GMPEs for the Indo-Burma subduction zone have been used to evaluate the hazard at the reference rock condition (Vs30 ​= ​760 ​m/s). Peak Ground Acceleration (PGA) and Spectral Acceleration (SA) at 0.2 s and 1s are estimated for each eight districts headquarters of Mizoram for a 2% and 10% probability of exceedance in 50 years. The hazard curves and Uniform Hazard Spectra (UHS) are also presented. For seismic risk analysis, building exposure data are based on digitized building footprint and 2011 Housing Census data of India. All the buildings are classified into three classes, and seismic vulnerability functions are assigned to each building class. The area per building class is assigned from the digitized footprint. Building replacement costs per square meter have been chosen based on expert input and values identified from past study. Lastly, the study conducted a seismic risk analysis using the Open Quake-engine's probabilistic event-based methodology to estimate risk metrics at the district level, such as average annual losses and probability curves for loss exceedance. The study's findings provide valuable insights into the most high-risk areas, the building construction types that are most vulnerable to seismic activity, and the anticipated economic losses in the state of Mizoram. These results can serve as a guide for local government authorities in developing future city plans and implementing earthquake risk mitigation strategies.

Updated probabilistic seismic hazard assessment of Pakistan

A probabilistic seismic hazard analysis of Pakistan is carried out to produce seismic hazard maps showing peak ground acceleration for the 2% and 10% of probability of exceedance in 50 years and spectral acceleration for the 5% and 2% probabilities of exceedance in 50 years. The main objective of this work is to define seismic hazard definition for Pakistan based on the classical approach using updated seismic hazards analysis inputs. A composite earthquake catalogue consisting of 32,700 events was compiled and used in the analysis with a magnitude range of Mw 4.0–8.3. The computations were made at a rectangular grid of 5 km in the OpenQuake engine. Ground motion parameter values have been obtained for flat rock reference seismic site conditions having a shear wave velocity of 760 m/s. Through the logic tree, epistemic uncertainties inherent in ground motion prediction equations and the maximum magnitude potential of seismic sources were estimated. Ground motion prediction equations were assigned equal weights in the logic tree while different weights were assigned to the maximum magnitude potential models. Results of the study were expressed as ground motion contour maps and median uniform hazard spectra for important cities in Pakistan. The results showed that peak ground acceleration values in Pakistan range from 0.16 to 0.54 g for the 10% of probability of exceedance, 0.23–0.72 g for the 5% probability of exceedance and 0.32–1.02 g for the 2% of probability of exceedance in 50 years. Spectral acceleration values at 0.2 s range from 0.67 to 2.19 g for the 2% chance of exceedance in 50 years, respectively, whereas spectral acceleration at 1.0 s ranges from 0.09 to 0.52 g for the 2% chance of exceedance in 50 years. The centre of Pakistan and the southern and the northern region are exposed to high hazard compared to the central-eastern part of the country. Quetta, Chitral, Peshawar, Islamabad Ziarat and Gwadar are exposed to seismic hazard in the PGA range of 0.32–0.45 g. Comparison of the results of this study with those of similar studies suggests that the seismic estimates proposed are reliable. The study provides a demonstration that the classical seismic hazard approach applied here is rational and applicable in Pakistan.

A national seismic risk model for Canada: Methodology and scientific basis

Canada is exposed to rare but potentially destructive earthquakes that threaten densely settled metropolitan centers in many parts of the country. To assess the impacts and consequences of future natural-hazard events and help advance policy goals and objectives of the Sendai Framework for Disaster Risk Reduction, Natural Resources Canada, through a collaborative partnership with the Global Earthquake Model Foundation, produced a national seismic risk model. Developing this model has required the creation of a national exposure inventory, Canadian-specific fragility and vulnerability curves, and significant simplification of the Canadian Seismic Hazard Model which forms the basis for the design seismic hazard values of the National Building Code of Canada. Using the Global Earthquake Model Foundation’s OpenQuake Engine, probabilistic stochastic risk modeling is completed under baseline and simulated retrofit conditions to assess seismic risk at the neighborhood level for all settled areas in Canada. Output risk metrics include the expected immediate physical impacts of earthquake events such as building damage, casualties, and direct economic losses. This article documents the technical details of the modeling approach including a description of novel data sets in use, a summary of the extensive sensitivity testing undertaken, and characterization of quality control implemented in the absence of usable validating earthquake loss data. The results from this model, such as loss exceedance curves and annual average losses, provide an open, accessible and quantitative base of evidence for decision-making at local, regional, and national levels. As a large country with a complex seismic hazard model and dispersed populations, this Canadian study is unique. However, the challenges faced and solutions offered are likely to be of interest to other nations pursuing similar programs.

Improving urban seismic risk estimates for Bishkek, Kyrgyzstan, through incorporating recently gained geological knowledge of hazards

Many cities are built on or near active faults, which pose seismic hazard and risk to the urban population. This risk is exacerbated by city expansion, which may obscure signs of active faulting. Here, we estimate the risk to Bishkek city, Kyrgyzstan, due to realistic earthquake scenarios based on historic earthquakes in the region and an improved knowledge of the active fault sources. We use previous literature and fault mapping, combined with new high-resolution digital elevation models to identify and characterise faults that pose a risk to Bishkek. We then estimate the hazard (ground shaking), damage to residential buildings and distribution of losses (economical cost and fatalities) using the Global Earthquake Model OpenQuake engine. We model historical events and hypothetical events on a variety of faults that could plausibly host significant earthquakes. This includes proximal, recognised, faults as well as a fault under folding in the north of the city that we identify using satellite DEMs. We find that potential earthquakes on faults nearest to Bishkek—Issyk Ata, Shamsi Tunduk, Chonkurchak and the northern fault—would cause the most damage to the city. An Mw 7.5 earthquake on the Issyk Ata fault could potentially cause 7900 ± 2600 completely damaged buildings, a further 16,400 ± 2000 damaged buildings and 2400 ± 1500 fatalities. It is vital to properly identify, characterise and model active faults near cities to reduce uncertainty as modelling the northern fault as a Mw 6.5 instead of Mw 6.0 would result in 37% more completely damaged buildings and 48% more fatalities.

The role of modelling of site conditions and amplification in seismic hazard and risk assessment at urban scale. The case of Thessaloniki, Greece

One of the main challenges of large-scale seismic hazard and risk applications is the characterization of the amplification of seismic ground motion due to the local site conditions, often described by Vs,30, i.e., the time- averaged shear wave velocity in the upper 30 meters of the soil deposit. In most of these applications, Vs,30 values are directly estimated from microzonation investigations, inferred from proxies such as the topographic slope, or obtained from seismic codes based on a simplified site categorization. The scope of this work is to investigate the effects of the method applied for modelling of site conditions and site amplification in urban risk assessment. For this we consider the application of the 2020 updates of the European Seismic Hazard (ESHM20) and Risk (ESRM20) Models and we focus on Thessaloniki, Greece, a city which is very well documented in terms of both local site conditions and exposure.To this end, we compare seismic hazard and risk results obtained using two different approaches for site conditions / site amplification modelling. In the first approach, which may be considered as more rigorous but also more demanding, two different appropriate site condition models are directly used in the ESHM20 hazard logic tree. In the second approach, which is more simplified and efficient in practice, two site amplification models were developed for the study area based on the soil classification according to two different code-oriented classification schemes. Eventually, four hazard models are obtained. Seismic risk results are presented in terms of expected damages and economic losses for a seismic hazard with a 475-year return period. Both hazard and risk assessment calculations are undertaken with the OpenQuake Engine (Pagani et al., 2014; Silva et al., 2014). The main conclusion for the case of Thessaloniki is that, for the given fragility and vulnerability models, the estimated aggregate damages and economic losses at city scale are not significantly affected by the way that local site conditions are taken into account, which indicates that simplified approaches for site modelling may be used for large scale applications when more rigorous approaches are not feasible. Significant discrepancies may occur, however, at local scale.

Exploring the impact of spatial correlations of earthquake ground motions in the catastrophe modelling process: a case study for Italy

Catastrophe models are important tools to provide proper assessment and financial management of earthquake-related emergencies, which still create the largest protection gap across all perils. Earthquake catastrophe models include three main components, namely: (1) the earthquake hazard model, (2) the exposure model and, (3) the vulnerability model. Simulating spatially distributed ground-motion fields within either deterministic or probabilistic seismic hazard assessments poses a major challenge when site-related financial protection products are required. In this framework, we develop ad hoc correlation models for different Italian regions (specifically northern, central and southern Italy) and thereafter we perform both deterministic scenario-based and probabilistic event-based hazard and risk assessments in order to advance the understanding of spatial correlations within the catastrophe modelling process. We employ the OpenQuake engine for our calculations. This is an open-source tool suitable for accounting for the spatial correlation of earthquake ground-motion residuals. Our outcomes, albeit preliminary, demonstrate the importance of considering not only the spatial correlation of ground motions, but also its associated uncertainty in risk analyses. Although loss exceedance probability curves for the return periods of interest for the (re)insurance industry show similar trends, both hazard and risk footprints in terms of average annual losses feature less noisy and more realistic patterns if spatial correlation is taken into account. Such results will have implications for (re)insurance companies evaluating the risk to high-value civil engineering infrastructures.

Time-dependent seismic hazard and risk due to wastewater injection in Oklahoma

In the past decade, Oklahoma has experienced unprecedented seismicity rates, following an increase in the volumes of wastewater that are being disposed underground. In this article, we perform a probabilistic assessment of the time-dependent seismic hazard in Oklahoma and incorporate these results into an integrated seismic risk model to assess the evolution of the statewide economic losses, including a conservative forecast through 2030. Our risk model employs an injection-driven earthquake rate model, a region-specific ground motion model, a recent Vs30 map, HAZUS exposure data and updated vulnerability curves for both structural and nonstructural elements, and contents. The calculations are performed using a stochastic Monte Carlo–based approach implemented in the OpenQuake engine. The resulting seismic hazard maps illustrate the incompatibility of the regional seismic provisions with the current seismicity. In 2015, in particular, the induced seismic hazard in several places in Oklahoma was higher than along the San Andreas fault. During the peak of seismicity in 2015, the seismic risk was 275 times higher than the background level, with the vast majority of losses originating from damages to nonstructural elements and contents. Our direct economic loss estimates are in reasonable agreement with the paid insurance claims, but show significant sensitivity to the ground motion model selection. The proposed risk model, with possible regular updates on the seismicity rate forecast, can help stakeholders define acceptable production levels.

Challenges and opportunities in New Zealand seismic hazard and risk modeling using OpenQuake

The corrected 2010 New Zealand National Seismic Hazard Model has been adapted for use in the Global Earthquake Model’s OpenQuake engine through an extensive benchmarking exercise with GNS Science’s legacy Fortran code. Resolution of differences between the legacy code and OpenQuake result in hazard curve output comparisons with discrepancies of less than 3% nationally and remaining discrepancies highlight challenges faced when moving away from in-house legacy code. OpenQuake’s multiple and varied computation options for both hazard and risk and OpenQuake’s consistent, software-friendly output formats allow for exploration and development of innovative approaches to future seismic hazard and risk modeling in New Zealand. The end-to-end seismic hazard-to-risk capabilities already enabled by the inclusion of New Zealand seismic hazard, vulnerability, and building exposure models in OpenQuake have already had significant impact on post-disaster response to the 2016 Kaikōura earthquake.

Probabilistic seismic risk assessment of India

This study presents a comprehensive open probabilistic seismic risk model for India. The proposed model comprises a nationwide residential and non-residential building exposure model, a selection of analytical seismic vulnerability functions tailored for Indian building classes, and the open implementation of an existing probabilistic seismic hazard model for India. The vulnerability of the building exposure is combined with the seismic hazard using the stochastic (Monte Carlo) event-based calculator of the OpenQuake engine to estimate probabilistic seismic risk metrics such as average annual economic losses and the exceedance probability curves at the national, state, district, and subdistrict levels. The risk model and the underlying datasets, along with the risk metrics calculated at different scales, are intended to be used as tools to quantitatively assess the earthquake risk across India and also compare with other countries to develop risk-informed building design guidelines, for more careful land-use planning, to optimize earthquake insurance pricing, and to enhance general earthquake risk awareness and preparedness.

Probabilistic seismic hazard assessment for Singapore

Seismic hazard assessment of metropolitan areas is an important topic in catastrophe risk management and disaster prevention. In this study, a probabilistic seismic hazard analysis (PSHA) is performed to estimate the seismic hazard for Singapore. The PSHA approach has been conducted based on the OpenQuake engine. An updated earthquake catalog for the neighboring region has been compiled from various sources, and three major source zones are identified using the updated earthquake catalog: Sumatra subduction zone, Sumatran strike–slip fault, and deformation–background zone. Also, 10 published ground motion prediction equations are incorporated in the logic-tree framework, which properly accounts for the epistemic uncertainty of ground motion intensity measures. The peak ground acceleration (PGA) values in the mean hazard maps at bedrock sites of Singapore for 10% and 2% exceedance probability in 50 years range from 0.04 to 0.05 g and from 0.14 to 0.15 g, respectively. The uniform hazard spectrum consisting of PGA and seven spectral accelerations is generated for rock sites in Singapore. Disaggregation analysis shows that the deformation zone identified contributes dominantly to the PGA hazard of Singapore, whereas the Sumatran strike–slip fault contributes dominantly to the long-period (spectral acceleration at 1.0 s) hazard. Besides, the seismic hazard maps for representative site conditions of Singapore are briefly presented.

PSHA software review based on the Monte Carlo method

The article is a continuation of the software research to perform probabilistic seismic hazard analysis (PSHA) as one of the main stages in engineering seismic surveys. The article provides an overview of modern software for PSHA based on the Monte Carlo method, describes in detail the work of foreign programs OpenQuake Engine and EqHaz. A test calculation of seismic hazard was carried out to compare the functionality of domestic and foreign software.

A probabilistic seismic hazard model for North Africa

African seismicity is predominantly localized along the East African Rift System (EARS), which is the major active tectonic feature of Sub-Saharan Africa. Besides the EARS, however, significant seismicity also occurs along a wide belt bounding the Mediterranean coastline. This tectonically active region extends discontinuously from Morocco to Egypt and its activity is controlled by the complex interaction between the Nubian and Eurasian plates, varying from transpression in the Atlas orogen in the west to transtension in the east. A record of large earthquake events is documented for the whole region, some of them causing moderate to severe levels of damage, mostly because of the high vulnerability of local buildings and structures, a condition which is still largely persistent in many areas. Currently, a number of seismic hazard models exist at local and national scales for North Africa, developed within independent projects and created using inhomogeneous data sources and different processing techniques. Unfortunately, such diversity makes their direct comparison problematic, obscuring the differences in seismic hazard across neighbouring areas and preventing the development of comprehensive long-term risk mitigation strategies. In fact, the last effort to produce a homogenized model for the whole Africa continent dates back to the GSHAP project, which is almost 20 years old. The creation of a unique seismic hazard model for North Africa, uniform across countries, is therefore a main concern. Since its inception, the Global Earthquake Model Foundation (GEM) is committed to the creation of a worldwide mosaic of high-quality, reproducible and openly accessible seismic hazard models, uniformly represented using the format adopted by the OpenQuake engine (OQ), a state-of-the-art, free and open-source software package for seismic hazard and risk assessment. We describe the development of a new comprehensive PSHA model for North Africa using GEM tools. The source model combines active faults and distributed seismicity, the former constrained from published geological descriptions and geodetic data, while the latter from the harmonisation of published earthquake catalogues.

Site-specific probabilistic seismic hazard of Prague (Czech Republic)

Prague is the capital of the Czech Republic with 1.3 million inhabitants. It is situated in an intraplate region with low seismicity. The seismic hazard is low, but not negligible. In its evaluation, we face the following challenging issues: (1) there have been no M > 6 events during the period covered by historical catalog (Giardini et al. 2013) although there is evidence from paleoseismic research of earthquakes with magnitude of at least 6.5. It is difficult to determine a reliable magnitude frequency distribution from sparse data. (2) There are no GMPEs determined from strong ground motion data for the region of interest. Therefore, we studied the attenuation from recent weak earthquakes in order to determine which of the published GMPEs are suitable for the region. (3) There are plenty of faults in the city and its neighborhood, all of them believed to be seismically inactive. We have to quantify the probability of an unexpected earthquake on such faults. We used the concept of diffused seismicity for this purpose. (4) The hazard is dominated by the 140 km distant West Bohemia Source Zone with earthquake swarm activity, which does not follow the classical mainshock-aftershock model. The results in the present study were obtained through the OpenQuake engine, the open-source software for seismic risk and hazard assessment developed within the global earthquake model (GEM) initiative. The seismic hazard for Prague (expressed in terms of peak ground acceleration) is below 0.1 g for the returning period of 10,000 years.

SHERIFS: Open‐Source Code for Computing Earthquake Rates in Fault Systems and Constructing Hazard Models

Modeling the seismic potential of active faults and their associated epistemic uncertainties is a fundamental step of probabilistic seismic-hazard assessment (PSHA). Seismic hazard and earthquake rate in fault systems (SHERIFS) is an open-source python code that builds hazard models including earthquake ruptures involving several fault sections or fault-to-fault (FtF) ruptures. It contains user-friendly tools to calculate the annual rate of FtF ruptures in a fault system based on the slip-rate estimates and accounting for associated background seismicity. SHERIFS applies a forward incremental approach following three rules: (1) the FtF ruptures allowed in the fault system are defined as input by the user and explored randomly, (2) the magnitude-frequency distribution of the modeled seismicity in the fault system must follow an imposed shape, and (3) the slip-rate budget attributed to each fault section must be preserved in the calculation if the first two rules allow it. Indeed, in some cases, a fraction of the slip-rate budget must be considered as being spent in non-mainshock events such as creep or postseismic slip. Background seismicity rates are defined by the hazard modeler as the ratio of seismicity occurring on the modelled faults for different ranges of magnitude. Given a coherent set of input hypotheses, SHERIFS allows end users to build the seismic-hazard fault model thanks to an interactive user-friendly interface. It aims to help interactions between field data collectors and hazard modelers to explore and weight epistemic uncertainties affecting the input hypotheses. To do so, SHERIFS includes tools to compare modeled earthquake rates with the available local data (earthquake catalog and paleoseismological data). This comparison can be used to weigh different hypotheses explored in a logic tree and discard the hypotheses that are not in agreement with the data. SHERIFS's outputs are in a format that can be used directly as inputs for PSHA in the OpenQuake engine (Pagani et al., 2014).

Combining USGS ShakeMaps and the OpenQuake‐engine for damage and loss assessment

SummaryThe evaluation of the potential impact of strong seismic events shortly after their occurrence is a critical step to organise emergency response and consequently minimise the adverse effects of earthquakes. The estimation of the impact from earthquakes considering the observed ground shaking from past events can be useful for the calibration of existing exposure and/or fragility and vulnerability models. This study describes a methodology to combine the publicly available information from the USGS ShakeMap system and the open‐source software OpenQuake engine for the assessment of damage and losses. This approach is employed to estimate the number of structural collapses considering the 2012 Magnitude 5.9 Emilia‐Romagna (Italy) earthquake and the aggregated economic loss because of the 2010 Magnitude 7.1 Darfield (New Zealand) event. Several techniques to calculate the ground shaking in the affected region considering the spatial and interperiod correlations in the intra‐event ground motion residuals are investigated and their influence in the resulting damage or loss estimates are evaluated.

Seismic Hazard Assessment of the Democratic Republic of Congo and Environs Based on the GEM–SSA Catalogue and a New Seismic Source Model

A new probabilistic seismic hazard assessment has been performed for the Democratic Republic of Congo (DRC) and surrounding areas. The DRC encompasses both intra-plate and active tectonic areas associated with the Congo Craton and the western branch of the East African Rift System, respectively. The seismic hazard assessment is based on the new Sub-Saharan-Global Earthquake Model Sub-Saharan–Global Earthquake Model earthquake catalogue with homogeneous magnitude representation (Mw) created by augmenting available global catalogues (e.g. International Seismological Center (ISC)-Reviewed, ISC–GEM, GCMT) with information from local agencies and regional projects, particularly from the AfricaArray network. This catalogue spans from 1900 to 2015. The initial declustered catalogue has 782 events. The historical earthquake record is sparse with significant variation in completeness over time across different regions. After taking the completeness of the catalogue into account, the final declustered catalogue used to calibrate the magnitude-frequency distribution of events used for the seismic hazard assessment spans 55 years (from 1960 to 2015) with 398 events and a magnitude of completeness of about 4.5. The maximum credible magnitude of earthquakes was determined using the entire catalogue from 1900 to 2015. The seismotectonic zonation into 15 seismic source areas was done on the basis of the regional geological structure, neotectonic fault systems, basin architecture and distribution of thermal springs and earthquake epicentres. Also, consideration was given to a regional strain rate model developed for the East African Rift by Saria et al. (Journal of Geophysical Research, 119, 3584–3600, 2014) in the frame of the GEM Strain Rate Project. Tectonic information was derived mostly from the scientific literature and by integration of available datasets. The current area source model consists of a total of 15 seismic zones distributed over 6 main tectonic groups that we assume to have comparable rheological and mechanical behavior with respect to the underlying crustal geology. The definition of these groups is essential for the regional calibration of b values. The b value is expected to be regionally stable with variations less than the uncertainty limits, while the activity rate λ is liable to vary substantially from one seismic source zone to another. The Gutenberg–Richter seismic hazard parameters were determined using Aki’s maximum likelihood method Aki (Bulletin of the Earthquake Research Institute, Tokyo University, 43, 237–239, 1965) and Weichert’s method Weichert (Bulletin of the Seismological Society of America, 70, 1337–1346, 1980), and compared with extension of the Aki-Utsu b value estimator for incomplete catalogues Kijko and Smit (Bulletin of the Seismological Society of America, 102, 1183–1287, 2012). Hazard computations were performed using the OpenQuake engine (version 2.7.0-1). The peak ground acceleration (PGA) and spectral acceleration at periods of 0.05, 0.1, 0.2, 0.5, 1 and 2 s was calculated using four ground motion prediction equations (GMPEs): two for active shallow crust Chiou et al. (Earthquake Spectra, 30, 1117–1153, 2014); Akkar et al. (Bulletin of Earthquake Engineering, 12, 359–387, 2014) and two for stable continental conditions Atkinson et al. (Bulletin of the Seismological Society of America, 96, 2181–2205, 2006; Pezeshk et al. (Bulletin of the Seismological Society of America, 101, 1859–1870, 2011) for soil sites corresponding to Vs 30 = 600, 760 and 1500 m/s at 11 cities of the DRC and surrounding areas. The results are consistent with those obtained using the regional frequency-independent attenuation law of Mavonga (Physics of the Earth and Planetary Interiors, 62, 13–21, 2007b) developed in the Kivu Rift segment and others Twesigomwe (Journal of African Earth Sciences, 24, 183–195, 1997), and Jonathan (Some aspects of seismicity in Zimbabwe and Eastern and Southern Africa. M.Sc. thesis. Institute of solid earth physics, Univ. Bergen, Bergen, Norway, pp. 100 (1996)), using Crisis 2012 software.