Is the sequence of earthquakes in Southern California, with aftershocks removed, Poissonian?

Gardner, J. K.; Knopoff, L.

doi:10.1785/bssa0640051363

Cited by 1,371 publications

(372 citation statements)

References 5 publications

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“…Our method is more straightforward than that of [10], because it does not require a sophisticated stochastic declustering procedure [12]. Still, it only needs to identify the events in a seismic sequence, in this work made with the classical [16] declustering algorithm. Despite its simplicity, our method gives encouraging good results.…”

Section: Discussionmentioning

confidence: 99%

“…The epicenter distribution of these events is shown in Figure 1. The current seismic sequences present in the seismic catalog have been detected by the [16] declustering algorithm, and the related parameters are provided and implemented in the ZMAP software [17]. Figure 2 shows the mainshocks (red dots) and foreshocks/aftershocks (blue dots) in three zones in the world (Chile, Mexico, and Indonesia).…”

Section: Datasetmentioning

confidence: 99%

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A New Smoothed Seismicity Approach to Include Aftershocks and Foreshocks in Spatial Earthquake Forecasting: Application to the Global Mw ≥ 5.5 Seismicity

Taroni

Akinci

2021

Applied Sciences

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Seismicity-based earthquake forecasting models have been primarily studied and developed over the past twenty years. These models mainly rely on seismicity catalogs as their data source and provide forecasts in time, space, and magnitude in a quantifiable manner. In this study, we presented a technique to better determine future earthquakes in space based on spatially smoothed seismicity. The improvement’s main objective is to use foreshock and aftershock events together with their mainshocks. Time-independent earthquake forecast models are often developed using declustered catalogs, where smaller-magnitude events regarding their mainshocks are removed from the catalog. Declustered catalogs are required in the probabilistic seismic hazard analysis (PSHA) to hold the Poisson assumption that the events are independent in time and space. However, as highlighted and presented by many recent studies, removing such events from seismic catalogs may lead to underestimating seismicity rates and, consequently, the final seismic hazard in terms of ground shaking. Our study also demonstrated that considering the complete catalog may improve future earthquakes’ spatial forecast. To do so, we adopted two different smoothed seismicity methods: (1) the fixed smoothing method, which uses spatially uniform smoothing parameters, and (2) the adaptive smoothing method, which relates an individual smoothing distance for each earthquake. The smoothed seismicity models are constructed by using the global earthquake catalog with Mw ≥ 5.5 events. We reported progress on comparing smoothed seismicity models developed by calculating and evaluating the joint log-likelihoods. Our resulting forecast shows a significant information gain concerning both fixed and adaptive smoothing model forecasts. Our findings indicate that complete catalogs are a notable feature for increasing the spatial variation skill of seismicity forecasts.

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Section: Discussionmentioning

confidence: 99%

Section: Datasetmentioning

confidence: 99%

A New Smoothed Seismicity Approach to Include Aftershocks and Foreshocks in Spatial Earthquake Forecasting: Application to the Global Mw ≥ 5.5 Seismicity

Taroni

Akinci

2021

Applied Sciences

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“…They tried to decluster the seismic event using different algorithm excluding aftershocks and foreshocks. Gardner and Knopoff (1974) designed a window based method for declustering in which they proposed that aftershocks located as succeeding shocks within specified distance and particular time interval. Same as in the case of foreshocks, succeeding foreshocks generate a large magnitude earthquake that will be treated as large aftershocks.…”

Section: Window Methods For Declusteringmentioning

confidence: 99%

“…The annual rate of seismicity of any region is based on the earthquake catalogue and number of earthquakes per year can be estimates using frequency magnitude relation (Gutenberg Richter law) associated with their a and b-values of specific region (Gutenberg and Richter, 1954, 1956a, 1956b. Different researchers proposed different procedures for declustering of earthquake catalogues (Knopoff and Gadner, 1972;Gardner and Knopoff, 1974;Reasenberg, 1985;Uhrhammer, 1986;Grunthal et al, 2009;Wiemer, 2001). A comprehensive detailed catalogue is the key to interpret the earthquake activity rate and analysis of occurrence and reoccurrence in the form of time series (Gupta et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

Statistical analysis of earthquake catalogue and magnitude of completeness for Northern and Southwestern Pakistan

Khurram¹

2021

Acta Geodynamica Et Geomaterialia

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A historical and instrumental earthquake catalogue is prepared for the Northwest Himalayan Fold and Thrust Belt and Makran Subduction Zone Pakistan from 1960 to 2019 with homogenized moment magnitude. The local and some international published sources were utilized for the preparation of catalogue. This earthquake catalogue contained numbers of duplicate, repeated, dependent and independent events. Declustering process was opted to remove the dependent events such as foreshock and aftershock from catalogue to separate the mainshock only in term of distance and time space window. The declustering found 2714 clusters of earthquakes with total of 19512 (57.19 %) events out of 34112. Only cluster events which contained the main shock or independent events were drawn on seismicity map with color identification. Maximum likelihood method was used to compute the value of magnitude of completeness i.e., Mc = 3.8 with estimation of a and b-values. Years vise magnitude of completeness was also computed to check the time period variation. The completeness of magnitude for different intervals of time indicates the impartial approximation of previous recorded seismicity. Temporal and spatial maps were also drawn to investigate the slope "b" and rate of productivity "a" in the study region. It is noted that b-values varied from 0.2 to 2.0 due to stress and intensive tectonic setting whereas a value increases due to increase the seismicity rate with respect to region. Seismotectonic map was drawn to delineate the major faults, seismicity pattern and tectonic activities. This work further can be used for single value hazard assessment for any region and their response spectra to update buildings and bridges codes.

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“…It spans a longer time period (till the end 2016) with a revised set of earthquakes, locations, and magnitude values. It includes only mainshocks recognized using the distance-and time-windowing declustering scheme of Gardner and Knopoff (1974). The present analysis was carried out for 63 mainshocks having the magnitude/time distribution shown in Figure 2B.…”

Section: Data Selectionmentioning

confidence: 99%

Statistical Relationship Between the Decrease of Major Seismicity and Drought in Southern California Since 1900

Bragato

2021

Front. Earth Sci.

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The seismicity in Southern California significantly decreased over the last decades. The decrease went in parallel with the reduction of meteoric groundwater recharge, which is a well-known factor capable of affecting seismicity. In this work the existence of a systematic statistical relationship was investigated by comparing the time density of Mw ≥ 5.7 earthquakes since 1900 with the time series of the Palmer Drought Severity Index (PDSI), an indicator of soil moisture roughly correlated with groundwater recharge. Given the non-stationarity of the two signals, the formal comparison was performed using both binomial logistic regression and cointegration testing. The analysis showed a significant statistical relationship, with peaks of seismicity 8 years behind those of PDSI. This finding suggests the hypothesis that groundwater recharge might affect earthquakes at a multi-year time scale. Proving this theory requires accurate measures and hydrogeological modeling, which is behind the scope of this work. Nonetheless, according to previous studies, the observed time lag might be explained by the slow propagation of pore pressure from the surface to the seismogenic volume. The ongoing trend towards an arid climate, made more evident by the recent severe droughts, might have contributed to the earthquake reduction of the last decades. The connection is particularly evident in the Salton Trough, with possible implications for the interpretation of its paleoseismicity.

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Is the sequence of earthquakes in Southern California, with aftershocks removed, Poissonian?

Abstract: Yes.

Cited by 1,371 publications

References 5 publications

A New Smoothed Seismicity Approach to Include Aftershocks and Foreshocks in Spatial Earthquake Forecasting: Application to the Global Mw ≥ 5.5 Seismicity

A New Smoothed Seismicity Approach to Include Aftershocks and Foreshocks in Spatial Earthquake Forecasting: Application to the Global Mw ≥ 5.5 Seismicity

Statistical analysis of earthquake catalogue and magnitude of completeness for Northern and Southwestern Pakistan

Statistical Relationship Between the Decrease of Major Seismicity and Drought in Southern California Since 1900

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