Stochastic Generator of Earthquakes for Mainland France

Mainland France is characterized by low-to-moderate seismic activity, yet it is known that major earthquakes could strike this territory (e.g., Liguria in 1887 or Basel in 1356). Assessing this French seismic hazard is thus necessary in order to support building codes and to lead prevention actions towards the population. The Probabilistic Seismic Hazard Assessment (PSHA) is the classical approach used to estimate the seismic hazard. One way to apply PSHA is to generate synthetic earthquakes by propagating information from past seismicity and building various seismic scenarios. In this paper, we present an implementation of a stochastic generator of earthquakes and discuss its relevance to mimic the seismicity of low-to-moderate seismic areas. The proposed stochastic generator produces independent events (main shocks) and their correlated seismicity (only aftershocks). Main shocks are simulated first in time and magnitude considering all available data in the area, and then localized in space with the use of a probability map and regionalization. Aftershocks are simulated around main shocks by considering both the seismic moment ratio and distribution of the aftershock’s proportion. The generator is tested with mainland France data.

Updated Probabilistic Seismic Hazard Assessment of Pakistan

Probabilistic seismic hazard assessment of Pakistan is carried out to compute hazard in terms of peak ground acceleration (PGA) and spectral acceleration (SA) for 975 and 2475 years return periods. A composite earthquake catalogue consisting of 32,700 events has been compiled having a magnitude range of Mw 4.0-8.2 in this study and used in the analysis to make computations at a rectangular grid of 5 km in the OpenQuake plateform. Ground motion values have been obtained for flat rock reference seismic site conditions with shear wave velocity of 760 m/s. The epistemic uncertainties inherent in ground motion prediction equations and maximum magnitude potential of seismic sources are taken into account through logic tree. Ground motion prediction equations are assigned equal weights in the logic tree while different various weight are assigned to the maximum magnitude potential models. Results of the study are expressed as ground motion contour maps, mean uniform hazard spectra for important cities in Pakistan. PGA ranges from 0.16 to 0.54g for 10 % of probability of exceedance, 0.23 to 0.72g of probability of exceedance 0.32 to 1.02 g for 2 % of probability of exceedance in 50 years. Spectral acceleration at 0.2 s range from 0.67 to 2.19g for 2% chance of exceedance in 50 years, respectively. While spectral acceleration at 1.0 s values range from 0.09 to 0.52g 2% chance of exceedance in 50 years. Comparison of results of this study with other well regarded references of suggest that results of the study are rational and are reliable.

Developing Earthquake-Resistant Structural Design Standard for Malaysia Based on Eurocode 8: Challenges and Recommendations

In late 2017, the Malaysian National Annex (NA) to Eurocode 8 (EC8) was released and enacted following some 13 years of deliberations and preparations. The authors of this paper aim to use this article to share their experiences and reflections during this period of developing the first national standard for the seismic design of buildings for Malaysia. To begin with, there were major challenges in implementing the 20-year-old EC8 framework for a country so far away from Europe. The first challenge was adapting the probabilistic seismic hazard assessment (PSHA) methodology in a low-to-moderate seismicity region where the paucity of representative seismic data presented a great deal of uncertainties. To address this situation, imposing a minimum level of seismic hazard was recommended. The second challenge was about dealing with the outdated EC8 site classification scheme, which poorly represents the potential effects of soil amplification in certain geological settings. To address this situation, an alternative site classification scheme in which the site natural period is an explicit modelling parameter was introduced. The third challenge was concerned with difficulties generated by the EC8 provisions mandating Ductility Class Medium (DCM) detailing in certain localities where the level of seismic hazard is predicted to exceed a certain threshold. To address this situation, the viable option of using strength to trade off for ductility was recommended, or in cases where ductility design is needed, a simplified set of code-compliant DCM designs was presented. The fourth challenge was about handling the requirements of EC8 that the majority of buildings are to involve dynamic analysis in their structural design when the majority of practising professionals did not have the skills of exercising proper use of the requisite software. To address this situation, a generalized force method was introduced to control the use dynamic analysis in commercial software. It is hoped that, through sharing the lessons learnt, code drafters for the future would be able to find ways of circumventing the multitude of challenges with clear thinking and pragmatism.

The Seismic Hazard Implications of Declustering and Poisson Assumptions Inferred from a Fully Time-Dependent Model

ABSTRACT We use the Third Uniform California Earthquake Rupture Forecast (UCERF3) epidemic-type aftershock sequence (ETAS) model (UCERF3-ETAS) to evaluate the effects of declustering and Poisson assumptions on seismic hazard estimates. Although declustering is necessary to infer the long-term spatial distribution of earthquake rates, the question is whether it is also necessary to honor the Poisson assumption in classic probabilistic seismic hazard assessment. We use 500,000 yr, M ≥ 2.5 synthetic catalogs to address this question, for which UCERF3-ETAS exhibits realistic spatiotemporal clustering effects (e.g., aftershocks). We find that Gardner and Knopoff (1974) declustering, used in the U.S. Geological Survey seismic hazard models, lowers 2% in 50 yr and risk-targeted ground-motion hazard metrics by about 4% on average (compared with the full time-dependent [TD] model), with the reduction being 5% at 40% in 50 yr ground motions. Keeping all earthquakes and treating them as a Poisson process increases these same hazard metrics by about 3%–12%, on average, due to the removal of relatively quiet time periods in the full TD model. In the interest of model simplification, bias minimization, and consideration of the probabilities of multiple exceedances, we agree with others (Marzocchi and Taroni, 2014) that we are better off keeping aftershocks and treating them as a Poisson process rather than removing them from hazard consideration via declustering. Honoring the true time dependence, however, will likely be important for other hazard and risk metrics, and this study further exemplifies how this can now be evaluated more extensively.

Integrated Seismic Hazard Analysis Of Southwest Penang Island Through Horizontal-To-Vertical Spectral Ratio And Probabilistic Seismic Hazard Assessment

Peninsular Malaysia is susceptible to large magnitude earthquakes induced by the regional sources as it is surrounded by countries that are known for their active seismicity. Tremors were felt in Penang Island of Pulau Pinang due to earthquake events in Sumatra, Indonesia in 2005 and 2009. Presence of cracks on buildings in the island was reported caused by the earthquake on 2nd November 2002. The tsunami that hit the island on 26 December 2004 was the aftermath of the Great Sumatra-Andaman earthquake with magnitude 9.1. The investigation of earthquake risks ensures that the effect of earthquake disasters in the inclined region can be reduced effectively. This paper aims to provide a comprehensive seismic hazard assessment in Penang Island by analysing the predominant natural frequency distribution in Balik Pulau through a passive seismic survey method known as horizontal-to-vertical spectral ratio (HVSR) and evaluating the ground motion throughout the island using probabilistic seismic hazard assessment (PSHA) approach. The natural frequencies of Balik Pulau mostly falls in the range of 3 to 4 Hz which is associated with loose deposits and stiff soil layer. The amplification factor extracted from the HVSR curves ranges approximately 4 to 5. The minimum ground motions estimated for a fixed intensity in 50 years for Penang Island is 0.006 g1 and can reach up to 0.025 g. While the minimum ground motions for a fixed return period of 98 years in 50 years is 0.016 g with maximum of 0.035 g.

Probabilistic seismic hazard assessment and site analyses of Arusha International Conference Centre (AICC), Arusha, Tanzania

This work presents the evaluation of earthquake resistance of the Arusha International ConferenceCentre (AICC) complex, in Tanzania. The evaluation included probabilistic seismic hazardanalysis (PSHA) and site response analysis. Seismic sources considered to constitute a seismichazard in this study were randomly occurring seismicity located within five tectonic provincesaround the site. For each province the seismic hazard is based on a cursory analysis of earthquakedata from compiled ESARSWG bulletins and temporary deployed networks within the NorthTanzania Divergence (NTD). Bedrock response signal together with the information of materialcharacteristics from boreholes around the AICC site were used in analysis of site response. PSHAresults indicated uniform hazard spectra values of 0.15, 0.2 and 0.27 g for return periods of 475,975 and 2475 years, respectively. The surface ground response results indicated a maximumamplification factor of 3.7 and a spectral response of 4.5 g for a wave period of 0.6 sec thatmatches the natural frequency of the 6-7 storey buildings of the AICC complex. It is thisresonance effect on the buildings that is assumed to have caused intense shaking in the earthquakeof December 5th 2005 from Lake Tanganyika. Keywords: Probabilistic seismic hazard analysis; Arusha International Conference Centre; EastAfrican Rift System; Uniform hazard spectra; Site effect.

Earthquake Rupture Forecasts for the MPS19 Seismic Hazard Model of Italy

In recent years, new approaches for developing earthquake rupture forecasts (ERFs) have been proposed to be used as an input for probabilistic seismic hazard assessment (PSHA). Zone- based approaches with seismicity rates derived from earthquake catalogs are commonly used in many countries as the standard for national seismic hazard models. In Italy, a single zone- based ERF is currently the basis for the official seismic hazard model. In this contribution, we present eleven new ERFs, including five zone-based, two smoothed seismicity-based, two fault- based, and two geodetic-based, used for a new PSH model in Italy. The ERFs were tested against observed seismicity and were subject to an elicitation procedure by a panel of PSHA experts to verify the scientific robustness and consistency of the forecasts with respect to the observations. Tests and elicitation were finalized to weight the ERFs. The results show a good response to the new inputs to observed seismicity in the last few centuries. The entire approach was a first attempt to build a community-based set of ERFs for an Italian PSHA model. The project involved a large number of seismic hazard practitioners, with their knowledge and experience, and the development of different models to capture and explore a large range of epistemic uncertainties in building ERFs, and represents an important step forward for the new national seismic hazard model.

Seismic hazard for the Trans Adriatic Pipeline (TAP). Part 2: broadband scenarios at the Fier Compressor Station (Albania)

To ensure environmental and public safety, critical facilities require rigorous seismic hazard analysis to define seismic input for their design. We consider the case of the Trans Adriatic Pipeline (TAP), which is a pipeline that transports natural gas from the Caspian Sea to southern Italy, crossing active faults and areas characterized by high seismicity levels. For this pipeline, we develop a Probabilistic Seismic Hazard Assessment (PSHA) for the broader area, and, for the selected critical sites, we perform deterministic seismic hazard assessment (DSHA), by calculating shaking scenarios that account for the physics of the source, propagation, and site effects. This paper presents a DSHA for a compressor station located at Fier, along the Albanian coastal region. Considering the location of the most hazardous faults in the study site, revealed by the PSHA disaggregation, we model the ground motion for two different scenarios to simulate the worst-case scenario for this compressor station. We compute broadband waveforms for receivers on soft soils by applying specific transfer functions estimated from the available geotechnical data for the Fier area. The simulations reproduce the variability observed in the ground motion recorded in the near-earthquake source. The vertical ground motion is strong for receivers placed above the rupture areas and should not be ignored in seismic designs; furthermore, our vertical simulations reproduce the displacement and the static offset of the ground motion highlighted in recent studies. This observation confirms the importance of the DSHA analysis in defining the expected pipeline damage functions and permanent soil deformations.