Shear-wave splitting associated with fluid processes beneath Styra, South Euboea: First results

IF 2.4 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS
Ioannis Spingos , George Kaviris , Vasilis Kapetanidis , Eleftheria Papadimitriou , Filippos Vallianatos
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引用次数: 0

Abstract

The intense and persistent seismic activity on the Island of Euboea (or Evia) was a unique opportunity to study anisotropy in a region without any notable prior seismicity. The study area is located in the central-western Aegean Sea and constitutes the endpoint where the North Aegean Trough and four parallel dextral strike-slip fault branches terminate against the Greek mainland, along with their sinistral counterparts. Even though seismicity has been recorded around the island, the affected area close to the town of Styra has no known reported earthquakes. In 2022, surprising activity was initiated by two moderate earthquakes (ML 4.8 and ML 5.0) that occurred on 29 November and were felt as far as Athens. The activity continued well into the second quarter of 2023, with over 1000 microearthquakes being recorded. A pre-planned nearby temporary installation of a broadband instrument (GR27), in the context of the AdriaArray project, offered recordings of the activity. Here, we investigated the occurrence and cause of shear-wave splitting beneath Styra. Based on focal mechanisms of local earthquakes we inferred the stress axes. A fully automated process was used to analyze data for shear-wave splitting and determine the polarization direction of the Sfast (φ), the time-delay (td) and the normalized time-delay (tn). A total of 272 acceptable results showcased a unimodal distribution of φ with an average of N68°E and a mean td of 80 ms. We observed temporal variations of splitting parameters, associated with outbursts of seismicity, not with individual events. The determination of the shear-wave velocity anisotropy, jointly with observations of other splitting parameters, led us to hypothesize that anisotropy is the result of along-fault fluid processes. However, this would require a convincing selection of the NE-SW nodal plane as the preferred fault orientation. Further enrichment of the catalogue and an increase in splitting results is required to draw more robust conclusions.

与南尤伯杯斯蒂拉地下流体过程有关的剪切波分裂:初步结果
爱奥博亚岛(或埃维亚岛)强烈而持续的地震活动为研究该地区的各向异性提供了一个独特的机会,而该地区此前并没有发生过任何明显的地震活动。研究区域位于爱琴海中西部,是北爱琴海海槽和四个平行的右旋走向滑动断层分支与希腊大陆的终点,同时也是其正弦对应断层的终点。尽管该岛周围有地震记录,但靠近斯蒂拉镇的受影响地区却没有已知的地震报告。2022 年,11 月 29 日发生的两次中度地震(ML 4.8 和 ML 5.0)引发了令人惊讶的地震活动,雅典也有震感。地震活动一直持续到 2023 年第二季度,共记录到 1000 多次微震。事先计划在附近临时安装的宽带仪器(GR27)为阿德里亚阵列项目提供了活动记录。在此,我们研究了斯蒂拉地下剪切波分裂的发生和原因。根据当地地震的焦点机制,我们推断了应力轴。我们采用全自动流程分析剪切波分裂数据,并确定 Sfast 的极化方向 (φ)、时间延迟 (td) 和归一化时间延迟 (then)。总共 272 项可接受的结果显示,φ 呈单峰分布,平均为 N68°E,平均 td 为 80 毫秒。我们观察到分裂参数的时间变化与地震爆发有关,而与单个事件无关。通过对剪切波速度各向异性的测定以及对其他劈裂参数的观测,我们推测各向异性是沿断层流体过程的结果。然而,这需要令人信服地选择东北-西南节理面作为首选断层方向。要得出更可靠的结论,还需要进一步丰富目录和增加分裂结果。
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来源期刊
Physics of the Earth and Planetary Interiors
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
78
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.
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