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Article ; Online: Implementing Non-Poissonian Forecasts of Distributed Seismicity into the 2022 Aotearoa New Zealand National Seismic Hazard Model

Iturrieta, P. / Gerstenberger, M. / Rollins, C. / Van Dissen, R. / Wang, T. / Schorlemmer, D.

Bulletin of the Seismological Society of America

2024

Abstract: Seismicity usually exhibits a non-Poisson spatiotemporal distribution and could undergo nonstationary processes. However, the Poisson assumption is still deeply rooted in current probabilistic seismic hazard analysis models, especially when input ... ...

Abstract	Seismicity usually exhibits a non-Poisson spatiotemporal distribution and could undergo nonstationary processes. However, the Poisson assumption is still deeply rooted in current probabilistic seismic hazard analysis models, especially when input catalogs must be declustered to obtain a Poisson background rate. In addition, nonstationary behavior and scarce earthquake records in regions of low seismicity can bias hazard estimates that use stationary or spatially precise forecasts. In this work, we implement hazard formulations using forecasts that trade-off spatial precision to account for overdispersion and nonstationarity of seismicity in the form of uniform rate zones (URZs), which describe rate variability using non-Poisson probabilistic distributions of earthquake numbers. The impact of these forecasts in the hazard space is investigated by implementing a negative- binomial formulation in the OpenQuake hazard software suite, which is adopted by the 2022 Aotearoa New Zealand National Seismic Hazard Model. For a 10% exceedance probability of peak ground acceleration (PGA) in 50 yr, forecasts that only reduce the spatial precision, that is, stationary Poisson URZ models, cause up to a twofold increase in hazard for low-seismicity regions compared to spatially precise forecasts. Furthermore, the inclusion of non-Poisson temporal processes in URZ models increases the expected PGA by up to three times in low-seismicity regions, whereas the effect on high-seismicity is minimal (∼5%). The hazard estimates presented here highlight the relevance, as well as the feasibility, of incorporating analytical formulations of seismicity that go beyond the inadequate stationary Poisson description of seismicity.
Subject code	519
Language	English
Publishing country	de
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Accounting for the Variability of Earthquake Rates within Low-Seismicity Regions

Iturrieta, P. / Gerstenberger, M. / Rollins, C. / Van Dissen, R. / Wang, T. / Schorlemmer, D.

Bulletin of the Seismological Society of America

Application to the 2022 Aotearoa New Zealand National Seismic Hazard Model

2024

Abstract: The distribution of earthquakes in time and space is seldom stationary, which could hinder a robust statistical analysis, particularly in low-seismicity regions with limited data. This work investigates the performance of stationary Poisson and spatially ...

Abstract	The distribution of earthquakes in time and space is seldom stationary, which could hinder a robust statistical analysis, particularly in low-seismicity regions with limited data. This work investigates the performance of stationary Poisson and spatially precise forecasts, such as smoothed seismicity models (SSMs), in terms of the available training data. Catalog bootstrap experiments are conducted to: (1) identify the number of training data necessary for SSMs to perform spatially better than the least-informative Uniform Rate Zone (URZ) models; and (2) describe the rate temporal variability accounting for the overdispersion and nonstationarity of seismicity. Formally, the strict-stationarity assumption used in traditional forecasts is relaxed into local and incremental stationarity (i.e., a catalog is only stationary in the vicinity of a given time point t) along with self-similar behavior described by a power law. The results reveal rate dispersion up to 10 times higher than predicted by Poisson models and highlight the impact of nonstationarity in assuming a constant mean rate within training-forecast intervals. The temporal rate variability is translated into a reduction of spatial precision by means of URZmodels. First, counting processes are devised to capture rate distributions, considering the rate as a random variable. Second, we devise a data-driven method based on geodetic strain rate to spatially delimit the precision of URZs, assuming that strain/stress rate is related to the timescales of earthquake interactions. Finally, rate distributions are inferred from the available data within each URZ. We provide forecasts for the New Zealand National Seismic Hazard Model update,which can exhibit rates up to ten times higher in low-seismicity regions compared with SSMs. This study highlights the need to consider nonstationarity in seismicity models and underscores the importance of appropriate statistical descriptions of rate variability in probabilistic seismic hazard analysis.
Subject code	519
Language	English
Publishing country	de
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Conference proceedings ; Online: Effects of Spatial Grid Resolution on the Statistical Power of Testing Earthquake Forecast Models

Khawaja, M. / Hainzl, S. / Iturrieta, P. / Schorlemmer, D.

Abstracts

2022

Abstract: The Collaboratory for the Study of Earthquake Predictability (CSEP) is an international effort to independently evaluate earthquake forecasting models and to provide the cyber-infrastructure together with a suite of testing methods. For global forecasts, ...

Abstract	The Collaboratory for the Study of Earthquake Predictability (CSEP) is an international effort to independently evaluate earthquake forecasting models and to provide the cyber-infrastructure together with a suite of testing methods. For global forecasts, CSEP defines a grid-based format to describe the expected rate of earthquakes, which is composed of 6.48 million cells for a 0.1º spacing. The spatial performance of the forecast is tested using the Spatial test (S-test), based on joint log-likelihood evaluations. The high-resolution grid combined with sparse and inhomogeneous earthquake distributions leads to many empty cells that may never experience an earthquake, biasing the S-test results. To explore this issue, we conducted a global earthquake forecast experiment. We tested a spatially uniform forecast model, which is non-informative and should be rejected by the S-test. However, it is not rejected by the S-test when the spatial resolution is high enough to allocate each observed earthquake in individual cells, thus raising questions about the test statistical power. The number of observed earthquakes used to evaluate global forecasts is usually only a few hundred, in contrast to the millions of spatial cells. Our analysis shows that for such disparity, the statistical power of tests for single-resolution grids also depends on the number of earthquakes available to evaluate a model. With few earthquakes, the S-test does not allow powerful testing. We propose to use a multi-resolution grid to generate and test earthquake forecast models, in which the resolution can be set freely based on available data, e.g., by the number of earthquakes per cell. Data-driven multi-resolution grids demonstrate the ability to reject the uniform forecast, contrary to a high-resolution grid. Furthermore, multi-resolution grids offer powerful testing with as minimum as four earthquakes available in the test catalog. Therefore, we propose to use multi-resolution grids in future CSEP global forecast experiments and to further ...
Language	English
Publishing country	de
Document type	Conference proceedings ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Fluid flow migration, rock stress and deformation due to a crustal fault slip in a geothermal system

Sáez-Leiva, F. / Hurtado, D. / Gerbault, M. / Ruz-Ginouves, J. / Iturrieta, P. / Cembrano, J.

Earth and Planetary Science Letters

A poro-elasto-plastic perspective

2023

Abstract: Geothermal systems are commonly genetically and spatially associated with volcanic complexes, which in turn, are located nearby crustal fault systems. Faults can alter fluid flow in their surroundings, potentially acting as barriers or conduits for ... ...

Abstract	Geothermal systems are commonly genetically and spatially associated with volcanic complexes, which in turn, are located nearby crustal fault systems. Faults can alter fluid flow in their surroundings, potentially acting as barriers or conduits for fluids, depending on their architecture and slip-rate. However, this fundamental control on fluid migration is still poorly constrained. Most previous modeling efforts on volcanic and hydrothermal processes consider either only fluid flow in their formulations, or only a mechanical approach, and seldom a full, monolithic coupling between both. In this work, we present a poro-elasto-plastic Finite Element Method (FEM) to address the first-order, time-dependent control that a strike-slip crustal fault exerts on a nearby geothermal reservoir. For the model setting, we selected the Planchón-Peteroa geothermal system in the Southern Andes Volcanic Zone (SAVZ), for which the geometry and kinematics of a potentially seismogenic fault and fluid reservoir is constrained from previous geological and geophysical studies. We assess the emergence and diffusion of fluid pressure domains due to fault slip, as well as the development of tensile/dilational and compressive/contractional domains in the fault' surroundings. Mean stress and volumetric strain magnitudes in these domains range between ±1 [MPa] and [-], respectively. Our results show the appearance of negative and positive fluid pressure domains in these dilational and contractional regions, respectively. We also investigate the spatial and temporal evolution of such domains resulting from changes in fault permeability and shear modulus, fluid viscosity, and rock rheology. These variations in fluid pressure alter the trajectory of the reservoir fluids, increasing migration to the eastern half of the fault, reaching a maximum fluid flux of 8 to 70 times the stationary flux. Pressure-driven fluid diffusion over time causes fluid flow to return to the stationary state between weeks to months after fault slip. These results ...
Subject code	532 ; 550
Language	English
Publishing country	de
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Conference proceedings ; Online: Coupled Poro-elasto-plastic models of transient fluid flow in response to a crustal strike-slip fault

Gerbault, M. / Saez Leiva, F. / Ginouvez, J. / Iturrieta, P. / Hurtado, D. / Cembrano, J.

Abstracts

insight from a geothermal setting in the South Andean volcanic zone

2023

Language	English
Publishing country	de
Document type	Conference proceedings ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Calculation of National Seismic Hazard Models with Large Logic Trees

DiCaprio, C. / Chamberlain, C. / Bora, S. / Bradley, B. / Gerstenberger, M. / Hulsey, A. / Iturrieta, P. / Pagani, M. / Simionato, M.

Seismological Research Letters

Application to the NZ NSHM 2022

2024

Abstract: National-scale seismic hazard models with large logic trees can be difficult to calculate using traditional seismic hazard software. To calculate the complete 2022 revision of the New Zealand National Seismic Hazard Model—Te Tauira Matapae Pūmate Rū i ... ...

Abstract	National-scale seismic hazard models with large logic trees can be difficult to calculate using traditional seismic hazard software. To calculate the complete 2022 revision of the New Zealand National Seismic Hazard Model—Te Tauira Matapae Pūmate Rū i Aotearoa, including epistemic uncertainty, we have developed a method in which the calculation is broken into two separate stages. This method takes advantage of logic tree structures that comprise multiple, independent logic trees from which complete realizations are formed by combination. In the first stage, we precalculate the independent realizations of the logic trees. In the second stage, we assemble the full ensemble of logic tree realizations by combining components from the first stage. Once all realizations of the full logic tree have been calculated, we can compute aggregate statistics for the model. This method benefits both from the reduction in the amount of computation necessary and its parallelism. In addition to facilitating the computation of a large seismic hazard model, the method described can also be used for sensitivity testing of model components and to speed up experimentation with logic tree structure and weights.
Subject code	511
Language	English
Publishing country	de
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Statistical power of spatial earthquake forecast tests

Khawaja, M. / Hainzl, S. / Schorlemmer, D. / Iturrieta, P. / Bayona, J. / Savran, W. / Werner, M. / Marzocchi, W.

Geophysical Journal International

2023

Abstract: The Collaboratory for the Study of Earthquake Predictability (CSEP) is an international effort to evaluate earthquake forecast models prospectively. In CSEP, one way to express earthquake forecasts is through a grid-based format: the expected number of ... ...

Abstract	The Collaboratory for the Study of Earthquake Predictability (CSEP) is an international effort to evaluate earthquake forecast models prospectively. In CSEP, one way to express earthquake forecasts is through a grid-based format: the expected number of earthquake occurrences within 0.1° × 0.1° spatial cells. The spatial distribution of seismicity is thereby evaluated using the Spatial test (S-test). The high-resolution grid combined with sparse and inhomogeneous earthquake distributions leads to a huge number of cells causing disparity in the number of cells, and the number of earthquakes to evaluate the forecasts, thereby affecting the statistical power of the S-test. In order to explore this issue, we conducted a global earthquake forecast experiment, in which we computed the power of the S-test to reject a spatially non-informative uniform forecast model. The S-test loses its power to reject the non-informative model when the spatial resolution is so high that every earthquake of the observed catalog tends to get a separate cell. Upon analysing the statistical power of the S-test, we found, as expected, that the statistical power of the S-test depends upon the number of earthquakes available for testing, e.g. with the conventional high-resolution grid for the global region, we would need more than 32 000 earthquakes in the observed catalog for powerful testing, which would require approximately 300 yr to record M ≥ 5.95. The other factor affecting the power is more interesting and new; it is related to the spatial grid representation of the forecast model. Aggregating forecasts on multi-resolution grids can significantly increase the statistical power of the S-test. Using the recently introduced Quadtree to generate data-based multi-resolution grids, we show that the S-test reaches its maximum power in this case already for as few as eight earthquakes in the test period. Thus, we recommend for future CSEP experiments the use of Quadtree-based multi-resolution grids, where available data determine the ...
Language	English
Publishing country	de
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Are Regionally Calibrated Seismicity Models More Informative than Global Models? Insights from California, New Zealand, and Italy

Bayona, J. / Savran, W. / Iturrieta, P. / Gerstenberger, M. / Graham, K. / Marzocchi, W. / Schorlemmer, D. / Werner, M.

The Seismic Record

2023

Abstract: Earthquake forecasting models express hypotheses about seismogenesis that underpin global and regional probabilistic seismic hazard assessments (PSHAs). An implicit assumption is that the comparatively higher spatiotemporal resolution datasets from which ...

Abstract	Earthquake forecasting models express hypotheses about seismogenesis that underpin global and regional probabilistic seismic hazard assessments (PSHAs). An implicit assumption is that the comparatively higher spatiotemporal resolution datasets from which regional models are generated lead to more informative seismicity forecasts than global models, which are however calibrated on greater datasets of large earthquakes. Here, we prospectively assess the ability of the Global Earthquake Activity Rate (GEAR1) model and 19 time‐independent regional models to forecast M 4.95+ seismicity in California, New Zealand, and Italy from 2014 through 2021, using metrics developed by the Collaboratory for the Study of Earthquake Predictability (CSEP). Our results show that regional models that adaptively smooth small earthquake locations perform best in California and Italy during the evaluation period; however, GEAR1, based on global seismicity and geodesy datasets, performs surprisingly well across all testing regions, ranking first in New Zealand, second in California, and third in Italy. Furthermore, the performance of the models is highly sensitive to spatial smoothing, and the optimal smoothing likely depends on the regional tectonic setting. Acknowledging the limited prospective test data, these results provide preliminary support for using GEAR1 as a global reference M 4.95+ seismicity model that could inform eight‐year regional and global PSHAs.
Language	English
Publishing country	de
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Conference proceedings ; Online: A physical constraint on smoothed-seismicity models and the stationary seismicity assumption in long-term forecasting

Iturrieta, P. / Schorlemmer, D. / Cotton, F. / Bayona, J. / Loviknes, K.

Abstracts

2020

Language	English
Publishing country	de
Document type	Conference proceedings ; Online
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Article ; Online: Effects of topography and basins on seismic wave amplification

García-Pérez, T. / Ferreira, A. / Yáñez, G. / Iturrieta, P. / Cembrano, J.

Geophysical Journal International

the Northern Chile coastal cliff and intramountainous basins

2021

Abstract: During earthquakes, structural damage is often related to soil conditions. Following the 2014 April 1 Mw 8.1 Iquique earthquake in Northern Chile, damage to infrastructure was reported in the cities of Iquique and Alto Hospicio. In this study, we ... ...

Abstract	During earthquakes, structural damage is often related to soil conditions. Following the 2014 April 1 Mw 8.1 Iquique earthquake in Northern Chile, damage to infrastructure was reported in the cities of Iquique and Alto Hospicio. In this study, we investigate the causes of site amplification in the region by numerically analysing the effects of topography and basins on observed waveforms in the frequency range 0.1–3.5 Hz using the spectral element method.We show that topography produces changes in the amplitude of the seismic waves (amplification factors up to 2.2 in the frequency range 0.1–3.5 Hz) recorded by stations located in steep areas such as the ca. 1-km-high coastal scarp, a remarkable geomorphological feature that runs north–south, that is parallel to the coast and the trench. The modelling also shows that secondary waves—probably related to reflections from the coastal scarp—propagate inland and offshore, augmenting the duration of the ground motion and the energy of the waveforms by up to a factor of three. Additionally, we find that, as expected, basins have a considerable effect on ground motion amplification at stations located within basins and in the surrounding areas. This can be attributed to the generation ofmultiple reflected waves in the basins, which increase both the amplitude and the duration ofthe ground motion, with an amplification factor of up to 3.9 for frequencies between 1.0 and 2.0 Hz. Comparisons between real and synthetic seismic waveforms accounting for the effects of topography and of basins show a good agreement in the frequency range between 0.1 and 0.5 Hz. However, for higher frequencies, the fit progressively deteriorates, especially for stations located in or near to areas of steep topography, basin areas, or sites with superficial soft sediments. The poor data misfit at high frequencies is most likely due to the effects ofshallow, small-scale 3-D velocity heterogeneity, which is not yet resolved in seismic images of our study region.
Subject code	551
Language	English
Publishing country	de
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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