{"title":"Space and time distribution of seismic source energy at Campi Flegrei, Italy through the last unrest phase (1.1.2000–31.12.2023)","authors":"Edoardo Del Pezzo , Francesca Bianco","doi":"10.1016/j.pepi.2024.107258","DOIUrl":null,"url":null,"abstract":"<div><p>We describe the space-time pattern of seismicity occurring on Campi Flegrei Caldera (CFC), Italy, where ground deformations and seismicity represent the drivers of its current bradyseismic crisis, well known and extensively studied at an international level. In detail we consider the seismicity in the time interval starting on 1.1.2000 and ending on 31.12.2023. We revise the statistics of the earthquake occurrence, focusing at possible precursory time changes of the b-parameter of the Gutenberg and Richter (G&R <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span>) distribution and at the time distribution of the total seismic moment inside any swarm. To estimate the G&R <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span> we use a Monte Carlo method instead of the ordinary Least Squares or Maximum likelihood methods, to easily measure the uncertainty on the <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span> taking into account uncertainties on the magnitude estimates. Results show that G&R <span><math><mi>a</mi><mo>−</mo><mi>value</mi></math></span> and <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span> calculated for cumulative and discrete distributions of <span><math><msub><mi>M</mi><mi>w</mi></msub></math></span>, the moment-magnitude, and <span><math><msub><mi>M</mi><mi>d</mi></msub></math></span>, the so-called duration-magnitude, are the same inside the uncertainties; <span><math><mi>a</mi><mo>−</mo><mi>value</mi></math></span> and <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span> for <span><math><msub><mi>M</mi><mi>d</mi></msub></math></span> are significantly different from the same parameters estimated for <span><math><msub><mi>M</mi><mi>w</mi></msub></math></span>, being <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span> for <span><math><msub><mi>M</mi><mi>w</mi></msub></math></span> close to the value of 1.0 and <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span> for <span><math><msub><mi>M</mi><mi>d</mi></msub></math></span> close to 0.8. The “bounded” G&R distribution fits the data yielding <span><math><mi>a</mi><mo>−</mo><mi>value</mi></math></span> and <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span> close to those for the unbounded distribution. The mean annual rate of exceedance, calculated for the entire catalogue, results to be 0.033<span><math><mo>±</mo><mn>0.015</mn></math></span> (years<sup>−1</sup>) corresponding to a return period of <span><math><mn>30</mn><mo>±</mo><mn>14</mn></math></span> years for <span><math><msub><mi>M</mi><mi>w</mi></msub><mo>=</mo><mn>4.5</mn></math></span>. The time dependence of G&R b-parameter show a <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span> time pattern characterized by variations slightly outside 1-<span><math><mi>σ</mi></math></span> uncertainty bar, tending to the value of 1 approaching present. As evidenced by several past studies, earthquakes in CFC occur in space-time clusters, with a mean time duration of 1 day. We selected the swarms with a selection algorithm, based on the joint estimation of inter-arrival times and inter-event distance for the consecutive event couples. The plot of the event number in each cluster vs the time of occurrence, clearly show that in CFC the number of cluster occurrences and the event number in each cluster accelerates during time starting from 2010. The time-pattern of the total seismic moment in each cluster shows that, contrarily to the event number, there is no evident striking increase of the total swarm moment as a function of time.</p><p>We also consider distribution of the Energy Space Density of the CFC earthquakes, ESD. This quantity shows a clearly visible enlargement of the fractured rock volumes in the last 15 months, toward West, at a depth around 3000 m below sea level. The most fractured zone coincides with the greatest contrasts in seismic attenuation.</p><p>The present study confirms that the current unrest phase is still ongoing, with an enlargement of the rock fracturing zone which extends southward and westward as compared with that measured 22 months before.</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"356 ","pages":"Article 107258"},"PeriodicalIF":2.4000,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S003192012400116X/pdfft?md5=a859af686a6ea4310c7c90813110214b&pid=1-s2.0-S003192012400116X-main.pdf","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Physics of the Earth and Planetary Interiors","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S003192012400116X","RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}
引用次数: 0
Abstract
We describe the space-time pattern of seismicity occurring on Campi Flegrei Caldera (CFC), Italy, where ground deformations and seismicity represent the drivers of its current bradyseismic crisis, well known and extensively studied at an international level. In detail we consider the seismicity in the time interval starting on 1.1.2000 and ending on 31.12.2023. We revise the statistics of the earthquake occurrence, focusing at possible precursory time changes of the b-parameter of the Gutenberg and Richter (G&R ) distribution and at the time distribution of the total seismic moment inside any swarm. To estimate the G&R we use a Monte Carlo method instead of the ordinary Least Squares or Maximum likelihood methods, to easily measure the uncertainty on the taking into account uncertainties on the magnitude estimates. Results show that G&R and calculated for cumulative and discrete distributions of , the moment-magnitude, and , the so-called duration-magnitude, are the same inside the uncertainties; and for are significantly different from the same parameters estimated for , being for close to the value of 1.0 and for close to 0.8. The “bounded” G&R distribution fits the data yielding and close to those for the unbounded distribution. The mean annual rate of exceedance, calculated for the entire catalogue, results to be 0.033 (years−1) corresponding to a return period of years for . The time dependence of G&R b-parameter show a time pattern characterized by variations slightly outside 1- uncertainty bar, tending to the value of 1 approaching present. As evidenced by several past studies, earthquakes in CFC occur in space-time clusters, with a mean time duration of 1 day. We selected the swarms with a selection algorithm, based on the joint estimation of inter-arrival times and inter-event distance for the consecutive event couples. The plot of the event number in each cluster vs the time of occurrence, clearly show that in CFC the number of cluster occurrences and the event number in each cluster accelerates during time starting from 2010. The time-pattern of the total seismic moment in each cluster shows that, contrarily to the event number, there is no evident striking increase of the total swarm moment as a function of time.
We also consider distribution of the Energy Space Density of the CFC earthquakes, ESD. This quantity shows a clearly visible enlargement of the fractured rock volumes in the last 15 months, toward West, at a depth around 3000 m below sea level. The most fractured zone coincides with the greatest contrasts in seismic attenuation.
The present study confirms that the current unrest phase is still ongoing, with an enlargement of the rock fracturing zone which extends southward and westward as compared with that measured 22 months before.
期刊介绍:
Launched in 1968 to fill the need for an international journal in the field of planetary physics, geodesy and geophysics, Physics of the Earth and Planetary Interiors has now grown to become important reading matter for all geophysicists. It is the only journal to be entirely devoted to the physical and chemical processes of planetary interiors.
Original research papers, review articles, short communications and book reviews are all published on a regular basis; and from time to time special issues of the journal are devoted to the publication of the proceedings of symposia and congresses which the editors feel will be of particular interest to the reader.