Continuous Gravity Observations at Campi Flegrei Caldera: An Accurate Assessment of Tidal and Non-Tidal Signals and Implications for Volcano Monitoring

IF 1.9 4区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS pure and applied geophysics Pub Date : 2024-09-05 DOI:10.1007/s00024-024-03555-4
U. Riccardi, T. Pivetta, A. Fedele, G. Ricciardi, S. Carlino
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Abstract

We present the results of nearly one year of gravity recording acquired at the active caldera of Campi Flegrei (CFc). CFc is one of the three active volcanoes in the Neapolitan area (southern Italy) and is currently the most active one. In fact, the CFc is undergoing a period of unrest characterised by slow uplift of the ground, a peculiar phenomenon known worldwide as bradyseism, accompanied by seismicity and intense fumarolic emissions. Due to the increased intensity of the volcano dynamics, a permanent gravity station equipped with a gPhoneX spring gravimeter was installed to enhance the geodetic monitoring programmes. The purpose of the continuous recordings is to complement the time-lapse observations carried out periodically on networks of benchmarks, in order to continuously monitor the short-term gravity signals. We report on the various processing steps and analyses performed to obtain reliable parameters of the Earth's tides, non-tidal corrections and gravity residuals. The various methodologies employed to investigate the instrumental drift are also elucidated in depth, because it may masquerade the elusive gravity changes resulting from mass fluctuations within the volcanic and geothermal systems. Residual gravity signals, retrieved from the recordings, after reduction of body and ocean tides, polynomial drift, atmospheric, tilt and change of the Earth Orientation Parameters (EOP) effects, appear to be uncorrelated with hydrology, while they show a clear correlation with the most energetic earthquakes, that strongly characterise the current bradyseismic crisis. The residual gravity signals display peculiar trends characterized by steps or offsets (up to about 600 nm/s2) and transients in coincidence of the most energetic volcano-tectonic events (Magnitude > 2.5) and seismic swarms. The steps in the gravity residuals are likely to be of instrumental origin, while the amplitudes of the observed transients are not consistent with co-seismic or volcanological phenomena, for which there is no evidence from other monitoring techniques. Unfortunately, the lack of repeated absolute gravity measurements severely limits our ability to attribute the observed gravity variations to geological sources. From the analysis of the gravity records, reliable tidal gravity models have been derived, which will improve the accuracy of volcano monitoring by allowing a precise reduction of tidal effects for both relative and absolute gravity measurements taken in these volcanic areas.

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坎皮弗莱格雷火山口的连续重力观测:潮汐和非潮汐信号的精确评估及其对火山监测的影响
我们展示了在坎皮弗莱格雷(CFc)活火山口进行的近一年的重力记录结果。CFc 是那不勒斯地区(意大利南部)三座活火山之一,也是目前最活跃的一座。事实上,CFc 火山正在经历一个动荡期,其特点是地面缓慢隆起,这种奇特的现象在全世界被称为 "缓动现象"(bradyseism),并伴有地震和强烈的炽热喷发。由于火山动态强度的增加,安装了一个配备 gPhoneX 弹簧重力仪的永久重力站,以加强大地测量监测计划。连续记录的目的是补充在基准网络上定期进行的延时观测,以持续监测短期重力信号。我们报告了为获得可靠的地球潮汐参数、非潮汐修正和重力残差而进行的各种处理步骤和分析。我们还深入阐释了调查仪器漂移所采用的各种方法,因为仪器漂移可能会掩盖火山和地热系统内部质量波动所导致的难以捉摸的重力变化。从记录中提取的残余重力信号,在减去体潮和海潮、多项式漂移、大气、倾斜和地球方位参数(EOP)变化的影响后,似乎与水文无关,但与能量最大的地震却有明显的相关性,这也是当前缓震危机的主要特征。残余重力信号显示出奇特的趋势,其特点是阶跃或偏移(高达约 600 nm/s2),以及与高能火山构造事件(震级为 2.5 级)和地震群相吻合的瞬变。重力残差中的阶跃很可能是由仪器引起的,而观测到的瞬态振幅与地震或火山现象不一致,其他监测技术也没有证据证明这一点。遗憾的是,由于缺乏重复的绝对重力测量,严重限制了我们将观测到的重力变化归因于地质来源的能力。通过对重力记录的分析,我们得出了可靠的潮汐重力模型,这将提高火山监测的准确性,因为在这些火山地区进行的相对重力和绝对重力测量都可以精确地减少潮汐效应。
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来源期刊
pure and applied geophysics
pure and applied geophysics 地学-地球化学与地球物理
CiteScore
4.20
自引率
5.00%
发文量
240
审稿时长
9.8 months
期刊介绍: pure and applied geophysics (pageoph), a continuation of the journal "Geofisica pura e applicata", publishes original scientific contributions in the fields of solid Earth, atmospheric and oceanic sciences. Regular and special issues feature thought-provoking reports on active areas of current research and state-of-the-art surveys. Long running journal, founded in 1939 as Geofisica pura e applicata Publishes peer-reviewed original scientific contributions and state-of-the-art surveys in solid earth and atmospheric sciences Features thought-provoking reports on active areas of current research and is a major source for publications on tsunami research Coverage extends to research topics in oceanic sciences See Instructions for Authors on the right hand side.
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