scholarly journals A sanity check for earthquake recurrence models used in PSHA of slow deforming regions: the case of SW Iberia

2020 ◽  
Author(s):  
Margarida Ramalho ◽  
Luis Matias ◽  
Marta Neres ◽  
Michele M. C. Carafa ◽  
Alexandra Carvalho ◽  
...  
Keyword(s):  
Seismic Moment ◽  
Seismic Risk ◽  
Seismic Hazard Assessment ◽  
Earthquake Source ◽  
Mitigation Measures ◽  
Probabilistic Seismic Hazard Assessment ◽  
Lower Tagus Valley ◽  
Source Models ◽  
Seismic Moment Release ◽  
Tagus Valley

Abstract. Probabilistic Seismic Hazard Assessment (PSHA) is the most common tool used to decide on the acceptable seismic risk and corresponding mitigation measures. We propose two consistency tests to address the variability of earthquake generation models found in PSHA studies: i) one rule-of-thumb test where the seismic moment release from the model is converted to an average slip on a typical fault and compared with known plate kinematics or GNSS deformation field; ii) using a neotectonic model, the computed deformation is converted into seismic moment release and to a synthetic earthquake catalogue. We apply these tests to the W and SW Iberia slow deforming region, where two earthquake source areas are investigated: 1) the Lower Tagus Valley, one of the largest seismic risk zones of Portugal; and 2) the offshore SW Iberia area, considered to be the source for the 1st November 1755 event (M~8.7). Results show that some of the earthquake source models should be considered as suspicious, given their high/low moment release when compared to the expected values from GNSS observations or neotectonic modelling. In conclusion, PSHA studies in slow deforming regions should include a similar sanity check on their models' evaluation, downgrading the weight of poorly compliant models.

A sanity check for earthquake recurrence models used in PSHA of slow deforming regions: the case of SW Iberia

2021 ◽  
Author(s):  
Margarida Ramalho ◽  
Luis Matias ◽  
Marta Neres ◽  
Michele M. C. Carafa ◽  
Alexandra Carvalho ◽  
...  
Keyword(s):  
Seismic Moment ◽  
Seismic Risk ◽  
Active Faults ◽  
Earthquake Source ◽  
Mitigation Measures ◽  
Probabilistic Seismic Hazard Assessment ◽  
Generation Model ◽  
Large Variability ◽  
Earthquake Generation ◽  
Seismic Moment Release

<p>Probabilistic Seismic Hazard Assessment (PSHA) is the most common tool used to decide on the acceptable seismic risk and corresponding mitigation measures. One key component of these studies is the earthquake generation model comprising the definition of source zones and recurrence relationships. Slow deforming regions are particularly challenging for PSHA since the inferred return period for large earthquakes is longer than the instrumental and historical seismicity records, and the relationship between known or probable active faults and seismicity is uncertain. Therefore, in these areas PSHA results show a large variability that impairs its acceptance by the political decision-makers and the public in general. We propose two consistency tests to address the variability of earthquake generation models found in PSHA studies: i) one rule-of-thumb test where the seismic moment release from the model is converted to an average slip on a typical fault and compared with known plate kinematics or GNSS deformation field; ii) using a neotectonic model, the computed deformation is converted into seismic moment release and to a synthetic earthquake catalogue. We apply these tests to the W and SW Iberia slow deforming region, where two earthquake source areas are investigated: 1) the Lower Tagus Valley, one of the largest seismic risk zones of Portugal; and 2) the offshore SW Iberia area, considered to be the source for the 1<sup>st</sup> November 1755 event (M~8.7). Our results show that some of the earthquake source models should be regarded as suspicious, given their high/low moment release when compared to the expected values from GNSS observations or neotectonic modelling. In conclusion, PSHA studies in slow deforming regions should include a similar sanity check on their models’ evaluation, downgrading the weight of poorly compliant models.</p>

scholarly journals Style of faulting of expected earthquakes in Italy as an input for seismic hazard modeling

2020 ◽  
Vol 20 (12) ◽  
pp. 3577-3592
Author(s):  
Silvia Pondrelli ◽  
Francesco Visini ◽  
Andrea Rovida ◽  
Vera D'Amico ◽  
Bruno Pace ◽  
...  
Keyword(s):  
Seismic Hazard ◽  
Seismic Moment ◽  
Outer Part ◽  
Seismic Hazard Assessment ◽  
Source Model ◽  
Probabilistic Seismic Hazard Assessment ◽  
Seismic Zone ◽  
Moment Tensors ◽  
Area Source ◽  
Seismic Moment Release

Abstract. The style of faulting and distributions of nodal planes are essential input for probabilistic seismic hazard assessment. As part of a recent elaboration of a new seismic hazard model for Italy, we defined criteria to parameterize the styles of faulting of expected earthquake ruptures and to evaluate their representativeness in an area-based seismicity model. Using available seismic moment tensors for relevant seismic events (Mw≥4.5), first arrival focal mechanisms for less recent earthquakes, and also geological data on past activated faults, we collected a database for the last ∼100 years by gathering a thousand data points for the Italian peninsula and regions around it. In this dataset, we adopted a procedure that consists, in each seismic zone, of separating the available seismic moment tensors into the three main tectonic styles, making a summation within each group, identifying possible nodal plane(s), taking into account the different percentages of styles of faulting, and including where necessary total or partial (even in terms of tectonic style) random source contributions. Referring to the area source model used, for several seismic zones we obtained robust results; e.g., along the central and southern Apennines we expect future earthquakes to be mostly extensional, although in the outer part of the chain reverse and strike-slip events are possible. In the northern part of the Apennines we expect different styles of faulting for different hypocentral depths. In zones characterized by a low seismic moment release, the possible style of faulting of future earthquakes is less clear and it has been represented using different combinations of random sources. The robustness of our results is confirmed when compared with recent relevant earthquakes occurring in Italy.

scholarly journals Tectonic styles of expected earthquakes in Italy as an input for seismic hazard modeling

2020 ◽  
Author(s):  
Silvia Pondrelli ◽  
Francesco Visini ◽  
Andrea Rovida ◽  
Vera D'Amico ◽  
Bruno Pace ◽  
...  
Keyword(s):  
Seismic Hazard ◽  
Seismic Moment ◽  
Outer Part ◽  
Seismic Hazard Assessment ◽  
Source Model ◽  
Probabilistic Seismic Hazard Assessment ◽  
Seismic Zone ◽  
Moment Tensors ◽  
Area Source ◽  
Tectonic Style

Abstract. Tectonic styles and distributions of nodal planes are an essential input for probabilistic seismic hazard assessment. As a part of a recent elaboration of a new seismic hazard model for Italy, we adopted a cascade criteria approach to parametrize the tectonic style of expected earthquake ruptures and their uncertainty in an area-based seismicity model. Using available or recomputed seismic moment tensors for relevant seismic events (Mw starting from 4.5), first arrival focal mechanisms for less recent earthquakes, and also geological data on past activated faults, we collected a database for the last ~ 100 yrs gathering a thousand of data all over the Italian peninsula and regions around it. The adopted procedure consists, in each seismic zone, of separating the available seismic moment tensors in the three main tectonic styles, making summation within each group, identifying possible nodal plane(s) taking into account the different percentages of tectonic styles and including, where necessary, total or partial random source contributions. Referring to the used area source model, for several seismic zones we obtained robust results, e.g. along the southern Apennines we expect future earthquakes to be mostly extensional, although in the outer part of the chain strike-slip events are possible. In the Northern part of the Apennines we also expect different tectonic styles for different hypocentral depths. In zones characterized by a low seismic moment release, the possible tectonic style of future earthquakes is less clear and it has been represented using different combination (total or partial) of random sources.

scholarly journals Bayesian validation of the seismic source models using the Wylfa Newydd site in the UK as a case study

2021 ◽  
Author(s):  
Ilaria Mosca ◽  
Brian Baptie ◽  
Manuela Villani ◽  
Z. Lubkowski ◽  
T. Courtney
Keyword(s):  
Seismic Hazard Assessment ◽  
Seismic Source ◽  
Probabilistic Seismic Hazard Assessment ◽  
Source Characterization ◽  
Statistical Tool ◽  
The United Kingdom ◽  
Nuclear Site ◽  
Seismic Source Models ◽  
Source Models ◽  
The Uk

Abstract In probabilistic seismic hazard assessment, the development of the seismic source characterization, especially the geometry of the seismic source models (SSMs), is controversial because it often relies on expert judgment with different interpretations of the available data from seismology, tectonics, and geology. Based on the same input datasets, different teams of experts may derive different SSMs. In this context, the verification of the models through the comparison against a set of observations is a crucial step. We present a statistical tool to compare the SSMs with the observed seismicity and rank these SSMs based on their ability to replicate the past seismicity. We simulate many synthetic catalogues derived from candidate SSMs and compare them with the observed catalogue of mainshocks using the Metropolis-Hastings Algorithm to select those that fit the observed catalogue. The candidate SSMs are then expressed by a probability density function (pdf) using the set of synthetic catalogues accepted by the Metropolis-Hastings Algorithm and the Bayesian inference. To help practitioners in earthquake and civil engineering understand how this tool works in practice, the proposed approach is applied to a proposed new nuclear site in the United Kingdom, Wylfa Newydd.

scholarly journals Development of seismicity and probabilistic hazard assessment for the Groningen gas field

2017 ◽  
Vol 96 (5) ◽  
pp. s235-s245 ◽  
Author(s):  
Bernard Dost ◽  
Elmer Ruigrok ◽  
Jesper Spetzler
Keyword(s):  
Hazard Assessment ◽  
Monitoring Network ◽  
Seismic Hazard Assessment ◽  
Velocity Model ◽  
Probabilistic Seismic Hazard Assessment ◽  
Gas Field ◽  
Ground Motion Model ◽  
Methods Of Calculation ◽  
Source Models ◽  
Groningen Gas Field

AbstractThe increase in number and strength of shallow induced seismicity connected to the Groningen gas field since 2003 and the occurrence of a ML 3.6 event in 2012 started the development of a full probabilistic seismic hazard assessment (PSHA) for Groningen, required by the regulator. Densification of the monitoring network resulted in a decrease of the location threshold and magnitude of completeness down to ~ ML=0.5. Combined with a detailed local velocity model, epicentre accuracy could be reduced from 0.5–1km to 0.1–0.3km and a vertical resolution ~0.3km. Time-dependent seismic activity is observed and taken into account into PSHA calculations. Development of the Ground Motion Model for Groningen resulted in a significant reduction of the hazard. Comparison of different implementations of the PSHA, using different source models, based on either a compaction model and production scenarios or on extrapolation of past seismicity, and methods of calculation, shows similar results.

scholarly journals Evaluating variability in coseismic slips of paleoearthquakes from an incomplete slip history: an example from displaced terrace flights across the Kamishiro fault, central Japan

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Naoya Takahashi ◽  
Shinji Toda
Keyword(s):  
Monte Carlo ◽  
Three Dimensional ◽  
Seismic Hazard Assessment ◽  
Probabilistic Seismic Hazard Assessment ◽  
Reverse Fault ◽  
Central Japan ◽  
Systematic Analysis ◽  
Fluvial Terraces ◽  
Rupture Length ◽  
Slip History

AbstractExamining the regularity in slip over seismic cycles leads to an understanding of earthquake recurrence and provides the basis for probabilistic seismic hazard assessment. Systematic analysis of three-dimensional paleoseismic trenches and analysis of offset markers along faults reveal slip history. Flights of displaced terraces have also been used to study slips of paleoearthquakes when the number of earthquakes contributing to the observed displacement of a terrace is known. This study presents a Monte Carlo-based approach to estimating slip variability using displaced terraces when a detailed paleoseismic record is not available. First, we mapped fluvial terraces across the Kamishiro fault, which is an intra-plate reverse fault in central Japan, and systematically measured the cumulative dip slip of the mapped terraces. By combining these measurements with the age of the paleoearthquakes, we estimated the amount of dip slip for the penultimate event (PE) and antepenultimate event (APE) to be 1.6 and 3.4 m, respectively. The APE slip was nearly three times larger than the most recent event of 2014 (Mw 6.2): 1.2 m. This suggests that the rupture length of the APE was much longer than that of the 2014 event and the entire Kamishiro fault ruptured with adjacent faults during the APE. Thereafter, we performed the Monte Carlo simulations to explore the possible range of the coefficient of variation for slip per event (COVs). The simulation considered all the possible rupture histories in terms of the number of events and their slip amounts. The resulting COVs typically ranged between 0.3 and 0.54, indicating a large variation in the slip per event of the Kamishiro fault during the last few thousand years. To test the accuracy of our approach, we performed the same simulation to a fault whose slip per event was well constrained. The result showed that the error in the COVs estimate was less than 0.15 in 86% of realizations, which was comparable to the uncertainty in COVs derived from a paleoseismic trenching. Based on the accuracy test, we conclude that the Monte Carlo-based approach should help assess the regularity of earthquakes using an incomplete paleoseismic record.

Sign in / Sign up

Export Citation Format

Share Document