Space and time distribution of seismic source energy at Campi Flegrei, Italy through the last unrest phase (1.1.2000–31.12.2023)

IF 2.4 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Physics of the Earth and Planetary Interiors Pub Date : 2024-09-17 DOI:10.1016/j.pepi.2024.107258

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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 $b - value$ ) distribution and at the time distribution of the total seismic moment inside any swarm. To estimate the G&R $b - value$ we use a Monte Carlo method instead of the ordinary Least Squares or Maximum likelihood methods, to easily measure the uncertainty on the $b - value$ taking into account uncertainties on the magnitude estimates. Results show that G&R $a - value$ and $b - value$ calculated for cumulative and discrete distributions of $M_{w}$ , the moment-magnitude, and $M_{d}$ , the so-called duration-magnitude, are the same inside the uncertainties; $a - value$ and $b - value$ for $M_{d}$ are significantly different from the same parameters estimated for $M_{w}$ , being $b - value$ for $M_{w}$ close to the value of 1.0 and $b - value$ for $M_{d}$ close to 0.8. The “bounded” G&R distribution fits the data yielding $a - value$ and $b - value$ close to those for the unbounded distribution. The mean annual rate of exceedance, calculated for the entire catalogue, results to be 0.033 $\pm 0.015$ (years⁻¹) corresponding to a return period of $30 \pm 14$ years for $M_{w} = 4.5$ . The time dependence of G&R b-parameter show a $b - value$ time pattern characterized by variations slightly outside 1- $σ$ 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.

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意大利坎皮弗莱格雷最后一个动荡阶段（2000 年 1 月 1 日至 2023 年 12 月 31 日）的震源能量时空分布情况

我们描述了发生在意大利坎皮弗莱格雷火山口（Campi Flegrei Caldera，CFC）的地震时空模式，地面变形和地震是该火山口当前缓震危机的驱动因素。我们详细考虑了从 2000 年 1 月 1 日到 2023 年 12 月 31 日这段时间内的地震情况。我们修订了地震发生的统计数据，重点关注古腾堡和里氏（G&R b 值）分布的 b 参数可能发生的前兆时间变化，以及任何震群内部总地震力矩的时间分布。为了估算 G&R b 值，我们使用蒙特卡罗方法而不是普通的最小二乘法或最大似然法，以便在考虑震级估算的不确定性的同时，轻松测量 b 值的不确定性。结果表明，在不确定性范围内，为时刻幅度 Mw 和持续时间幅度 Md 的累积分布和离散分布计算出的 G&R a 值和 b 值是相同的；Md 的 a 值和 b 值与 Mw 的相同参数估计值有显著差异，Mw 的 b 值接近 1.0，Md 的 b 值接近 0.8。有界 "G&R 分布与数据拟合，得出的 a 值和 b 值与无界分布接近。计算整个目录的年平均超标率为 0.033±0.015（年-1），对应于 Mw=4.5 时 30±14 年的回归期。G&R b参数的时间依赖性显示了一个b值时间模式，其特点是变化略微超出1-σ的不确定性条，趋向于接近1的值。过去的一些研究表明，CFC 地震发生在时空群中，平均持续时间为 1 天。我们根据对连续事件偶的到达时间和事件间距离的联合估计，用选择算法选出了地震群。每个群中的事件数与发生时间的对比图清楚地表明，在 CFC 中，从 2010 年开始，群发生的次数和每个群中的事件数都在加速增长。每个震群的总地震力矩的时间模式表明，与事件数相反，震群总地震力矩并没有随着时间的推移而明显增加。这一数据显示，在过去的 15 个月中，断裂岩石体积明显向西扩大，深度在海平面以下 3000 米左右。本研究证实，当前的动荡阶段仍在持续，与 22 个月前相比，岩石断裂带向南、向西扩展。

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来源期刊

Physics of the Earth and Planetary Interiors 地学天文-地球化学与地球物理

CiteScore

5.00

自引率

4.30%

发文量

审稿时长

18.5 weeks

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.