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Multimodal quantitative segmental analysis of seismicity of the Zhangjiakou-Bohai tectonic belt (North China) 张家口-渤海构造带(华北)地震多模态定量分段分析
IF 1.6 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2024-08-02 DOI: 10.1007/s10950-024-10234-3
Jinmeng Bi, Cheng Song, Fuyang Cao, Yong Ma

The purpose of this study is to systematically investigate the segmental seismicity features of the Zhangjiakou-Bohai tectonic belt to understand the characteristics of the seismic activity in this tectonic area and identify potential sources of strong earthquake hazard. From the collected seismic data, we first determined the minimum completeness magnitude by combining qualitative and quantitative methods, such as the detection rate function, maximum curvature (MAXC) method, goodness of fit (GFT) method and magnitude-rank method. We used the stochastic declustering method based on the space-time ETAS model to obtain the background seismicity. We then implemented the accelerating moment release (AMR) model, the Ogata-Katsura 1993 (OK1993) model, the moment ratio (MR) model and the Region-Time-Length (RTL) algorithm. Finally, we analyzed the spatial migration of strong earthquakes. The completeness magnitude of the earthquake sequence does not significantly change with time, with the minimum completeness magnitude being 2.0 for the Zhangjiakou-Bohai tectonic zone. The results provided by the aforementioned seismic activity models allow us to detect some differences between sectors of the tectonic belt. The Zhangjiakou and Tangshan segments show a higher level of seismic hazard compared to the others, which have little chance of a strong earthquake occurring (weak release of seismic energy). The b value of the Zhangjiakou segment shows a stepwise downward trend, reflecting the gradual increase of stress accumulation level, and the hazard of moderate-strong earthquakes is increasing. Compared with the Tangshan and Penglai segments, the Zhangjiakou and Beijing sectors have a slightly higher MR index, which means that the rate of earthquake occurrence is increasing and thus the hazard of moderate to strong earthquakes. According to the RTL value, the deviation of seismic activity in the Zhangjiakou and Tangshan segments is relatively high, and there is a possibility of moderate to strong earthquakes in the future. Based on the results obtained from various seismicity models and the migration law of strong earthquakes, we can say that the overall seismic hazard for each sector of the Zhangjiakou-Bohai tectonic chain is low in terms of qualitative analysis. If anything, the Zhangjiakou segment, which is the section with the relatively high seismic hazard level, should require our attention in the future.

本研究旨在系统研究张家口-渤海构造带的节段地震活动性特征,以了解该构造带的地震活动特征,识别潜在的强震危险源。根据收集到的地震数据,我们首先结合检波率函数、最大曲率法(MAXC)、拟合优度法(GFT)和震级秩方法等定性和定量方法,确定了最小完全震级。我们使用基于时空 ETAS 模型的随机解簇法获得背景地震度。然后,我们采用了加速矩释放(AMR)模型、Ogata-Katsura 1993(OK1993)模型、矩比(MR)模型和区域-时间-长度(RTL)算法。最后,我们分析了强震的空间迁移。地震序列的完整性震级随时间变化不大,张家口-渤海构造带的最小完整性震级为 2.0。根据上述地震活动性模型提供的结果,我们可以发现构造带不同区段之间的一些差异。张家口和唐山地段与其他地段相比,地震危险性较高,发生强震的可能性较小(地震能量释放较弱)。张家口段的 b 值呈阶梯式下降趋势,反映了应力累积水平的逐步提高,中强地震的危险性在增大。与唐山段和蓬莱段相比,张家口段和北京段的 MR 指数略高,这说明地震发生率在增加,因而中强地震的危险性也在增加。根据 RTL 值,张家口段和唐山段的地震活动偏差相对较大,未来有可能发生中强地震。根据各种地震活动性模型得出的结果和强震的迁移规律,我们可以说,从定性分析的角度看,张家口-渤海构造链各段的总体地震危险性较低。如果说张家口地段是地震危险性相对较高的地段的话,那么张家口地段的地震危险性就需要我们在今后的工作中加以重视。
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引用次数: 0
Numerical simulation of near-fault ground strains and rotations from actual earthquakes with predominantly dip-slip mechanisms 以数值模拟以倾滑机制为主的实际地震产生的近断层地层应变和旋转
IF 1.6 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2024-07-29 DOI: 10.1007/s10950-024-10230-7
Yenan Cao, George P. Mavroeidis

In the absence of records of near-fault ground strains and rotations from strong earthquakes, deterministic physics-based simulations have become an important tool for characterizing these motions in the low-frequency range (e.g., < 1.0 Hz). Building on a previous study of near-fault ground strains and rotations from actual strike-slip ruptures conducted by the authors, this article investigates the spatial and temporal characteristics of such motions generated by actual earthquakes with predominantly dip-slip mechanisms. This is achieved by performing forward ground-motion simulations of the 1994 Mw 6.7 Northridge, the 1989 Mw 6.9 Loma Prieta, and the 1985 Mw 8.1 Michoacan earthquakes using previously published finite-fault rupture models. For each considered seismic event, time histories of ground strains and rotations are generated at near-fault recording stations and at a dense grid of observation points. This is accomplished by finite differencing translational motions simulated at very closely spaced stations using a kinematic modeling approach. The simulation results show large-amplitude axial strain, shear strain, and rocking in the near-fault region. For the considered earthquakes, the maximum peak ground strain over all grid points is of the order of ~ 100–250 μstrain, whereas the maximum peak ground rocking ranges from ~ 100 to ~ 200 μrad. The attenuation characteristics of peak ground strains and rotations differ for the considered seismic events and depend on the component of interest and the rupture distance. Finally, peak ground rocking can be reasonably estimated from peak vertical ground velocity using a properly selected scaling factor despite the significant variability of the latter in the near-fault region. Filtering out the very low frequencies of ground motion (< 0.1 Hz), including the static offset, significantly affects the scaling factor.

由于缺乏强地震近断层地面应变和旋转的记录,基于确定性物理学的模拟已成为描述低频范围(如 1.0 Hz)内这些运动特征的重要工具。本文以作者之前对实际击滑断裂产生的近断层地应变和旋转进行的研究为基础,研究了以倾滑机制为主的实际地震产生的此类运动的空间和时间特征。为此,作者使用之前发布的有限断层破裂模型对 1994 年 Mw 6.7 北岭地震、1989 年 Mw 6.9 洛马普列塔地震和 1985 年 Mw 8.1 米却肯地震进行了前向地动模拟。对于每个考虑的地震事件,都会在近断层记录站和密集的观测点网格上生成地面应变和旋转的时间历程。这是通过有限差分平移运动来实现的,平移运动是利用运动学建模方法在间距很近的台站进行模拟的。模拟结果显示了近断层区域的大振幅轴向应变、剪切应变和摇晃。对于所考虑的地震,所有网格点的最大地应变峰值约为 100-250 μstrain ,而最大地摇动峰值则在约 100 至约 200 μrad 之间。对于所考虑的地震事件,峰值地应变和地震动的衰减特性各不相同,并取决于相关成分和破裂距离。最后,尽管地震动峰值在近断层区有很大的变异性,但可以利用适当选择的缩放因子,从垂直地动速度峰值中合理地估算出地震动峰值。过滤掉极低频率的地面运动(0.1 赫兹),包括静态偏移,会对比例因子产生重大影响。
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引用次数: 0
Characterization of seismic b-value around kopili fault and its neighboring region prior to 28th April 2021 earthquake 2021 年 4 月 28 日地震前科皮里断层及其邻近地区的地震 b 值特征
IF 1.6 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2024-07-20 DOI: 10.1007/s10950-024-10232-5
Vickey Sharma, Dipok Kumar Bora, Devajit Hazarika, Rajib Biswas

In the present study, the spatio-temporal variation of the seismic b-value in the vicinity of the Kopili fault and its surrounding area has been analysed using the unified and homogenous earthquake catalog of historical and instrumental (1950–2021) earthquake events. The study region is subdivided into 16 equisized square grids of 1° × 1° dimension, and the b-value is computed for each grid using the maximum likelihood method. The spatial distribution of the b-value varies from 0.58 to 1.14. The Kolmogorov–Smirnov (K-S) test has been conducted to check the significance of the spatial-temporal and depth-wise distributions of the b-value. The epicentral location of April 28th, 2021, lies in the low-b-value square grid. Likewise, the temporal b-value curve shows a decreasing trend before the occurrence of the April 28th, 2021 earthquake. The mean return period of the April 28th, 2021earthquake and the most probable maximum annual magnitude earthquake are also computed for this region. Meanwhile, the spatial associations and anomalous patterns between the b-value and factors like seismic moment or energy release and focal depth are assessed, as they contribute to a more comprehensive understanding of the seismicity in this area. The antithetical relationship between the b-value and seismic moment or energy release is established. While variation in b-value with depth provides new insights, low b-values are linked to the top of the crust, which could mean that the crust is uniform and that a lot of stress is building up.

在本研究中,利用历史和仪器地震事件(1950-2021 年)的统一和同质地震目录,分析了科皮里断层附近及其周边地区地震 b 值的时空变化。研究区域被细分为 16 个尺寸为 1° × 1° 的等化正方形网格,并使用最大似然法计算每个网格的 b 值。b 值的空间分布从 0.58 到 1.14 不等。对 b 值的时空分布和深度分布进行了 Kolmogorov-Smirnov (K-S) 检验。2021 年 4 月 28 日的震中位置位于低 b 值方格网中。同样,在 2021 年 4 月 28 日地震发生之前,时间 b 值曲线也呈下降趋势。此外,还计算了该区域 2021 年 4 月 28 日地震的平均重现期和最可能发生的最大年震级地震。同时,评估了 b 值与地震力矩或能量释放、焦深等因素之间的空间关联和异常模式,这有助于更全面地了解该地区的地震活动性。确定了 b 值与地震力矩或能量释放之间的反比关系。虽然 b 值随深度的变化提供了新的见解,但低 b 值与地壳顶部有关,这可能意味着地壳是均匀的,大量应力正在积聚。
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引用次数: 0
Revisiting Stepp’s method for the completeness of regional seismic catalogues 重新审视斯泰普的区域地震目录完整性方法
IF 1.6 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2024-07-18 DOI: 10.1007/s10950-024-10231-6
Narsiram Gurjar, Dhiman Basu

An important step in seismic hazard analysis is investigating the completeness of available data. Out of the various methods proposed by several researchers, Stepp’s method is one of the most commonly used methods for completeness analysis. Some drawbacks are identified in this method, which results in erroneous estimation of the completeness period. This paper suggests another way of estimation based on the 2-point moving average of the mean annual rate of occurrence of events. The new procedure is able to overcome the problems identified in Stepp’s method and is validated using five catalogues from different regions. The analysis result includes the completeness period determination for different catalogues before and after correction, together with Magnitude-Frequency recurrence relation coefficients compared with Stepp’s method.

地震灾害分析的一个重要步骤是调查可用数据的完整性。在一些研究人员提出的各种方法中,Stepp 方法是最常用的完备性分析方法之一。这种方法存在一些缺点,导致对完整性周期的估计错误。本文提出了另一种基于事件平均年发生率两点移动平均值的估算方法。新程序能够克服 Stepp 方法中发现的问题,并使用来自不同地区的五个星表进行了验证。分析结果包括校正前后不同星表的完整周期测定,以及与 Stepp 方法相比较的震级-频率重现关系系数。
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引用次数: 0
Comparison between rupture parameters of intermediate and deep earthquakes at the Peru–Brazil–Bolivia border and northern Chile 秘鲁-巴西-玻利维亚边境和智利北部中深层地震破裂参数的比较
IF 1.6 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2024-07-09 DOI: 10.1007/s10950-024-10229-0
Carmen Pro, Hernando Tavera, Maurizio Mattesini, Lucía Escudero, Elisa Buforn, Agustín Udías, Estela Centeno

We determined the main parameters of the source rupture process of intermediate- and deep-depth earthquakes occurring in the Peru–Brazil–Bolivia border region and northern Chile. The parameters of depth, fault-plane orientation, scalar seismic moment, slip distribution, and radiated seismic energy are obtained from seismograms. We selected 15 intermediate-depth earthquakes (100 km < h < 300 km) and 10 very deep earthquakes (h > 500 km) with magnitudes MW ≥ 6.0. For most events, the slip distribution over the rupture plane shows a single asperity, and the source time function presents a simple pulse. There are differences between intermediate-depth and deep earthquakes. The rupture areas, maximum slip and source time function (STF) duration are larger for intermediate-depth events than for deep events. Additionally, the STF’s show a sharper increase for deep earthquakes. The scaled radiated seismic energy shows larger values for deep depth events. The stress regime pattern derived from the obtained focal mechanism agrees with the geometry of the subduction of the Nazca plate. At intermediate depths, in the northern area up to 12°S, the stress pattern corresponds to a horizontal extension, while in the southern area, the tension axes dip at an angle of 30°. At deep depths, the stress regime corresponds to vertical compression in the north and dips of approximately 45° in the south.

我们确定了发生在秘鲁-巴西-玻利维亚边境地区和智利北部的中深层地震震源破裂过程的主要参数。深度、断层面方位、标量地震力矩、滑移分布和辐射地震能量等参数都是通过地震图获得的。我们选择了 15 次中深度地震(100 km < h < 300 km)和 10 次超深地震(h > 500 km),震级 MW ≥ 6.0。对于大多数地震事件,破裂面上的滑移分布显示为单一斜面,震源时间函数显示为简单脉冲。中深层地震和深层地震之间存在差异。与深层地震相比,中层地震的破裂面积、最大滑移和震源时间函数(STF)持续时间更大。此外,深层地震的震源时间函数(STF)增长更快。按比例辐射的地震能量显示深层地震的数值更大。根据所获得的焦点机制得出的应力机制模式与纳斯卡板块俯冲的几何形状相吻合。在中等深度,即南纬 12 度以内的北部地区,应力模式相当于水平延伸,而在南部地区,张力轴倾角为 30 度。在深层,北部的应力机制相当于垂直压缩,而南部的应力机制则倾角约为 45°。
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引用次数: 0
Spatiotemporal properties of the 2020 – 2021 Petrinja (Croatia) earthquake sequence 2020 - 2021 年佩特里尼亚(克罗地亚)地震序列的时空特性
IF 1.6 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2024-07-01 DOI: 10.1007/s10950-024-10228-1
Eirini Sardeli, Georgios Michas, Kyriaki Pavlou, Davide Zaccagnino, Filippos Vallianatos

The Petrinja earthquake sequence started on December 28, 2020, with a destructive ML 6.2 mainshock occurring in the area, preceded by a ML 5.08 foreshock, following a long period of relative seismic quiescence. Over the first six months of the Petrinja earthquake sequence, almost 14,000 events were recorded. In the present work, we separated seismic events based on their spatial concentration using a density-based clustering algorithm, DBSCAN. We identified four main clusters and analyzed their spatiotemporal properties using the notions of Non-Extensive Statistical Physics (NESP). This framework, which relies on Tsallis entropy (Sq), describes the scaling behavior of complex systems. In this frame, we investigated the inter-event time (T) and distance (D) distributions, providing the qT and qD entropic parameters, respectively. Additionally, we studied the frequency–magnitude distributions in terms of the fragment–asperity model, leading to the determination of the non-extensive parameter qM. The results of the analysis suggest that the statistical properties of the Petrinja earthquake sequence can be effectively reproduced utilizing NESP. Furthermore, the coseismic static Coulomb stress changes were estimated, indicating that the clusters’ seismic events may have resulted from a complex fault system's (re)activation. In addition, the effective static stress drop was estimated for each spatial cluster. Lastly, the temporal patterns of the earthquake evolution are discussed using the superstatistics approach, indicating that the temporal progression of the Petrinja earthquake clusters is governed by a very low number of degrees of freedom, highlighting the spatiotemporal organization of each cluster.

佩特里尼亚地震序列始于 2020 年 12 月 28 日,在该地区发生了一次破坏性的 ML 6.2 主震,在此之前发生了一次 ML 5.08 前震,此前该地区长期处于相对地震静止状态。在 Petrinja 地震序列的前六个月中,记录了近 14,000 次地震事件。在本研究中,我们使用基于密度的聚类算法 DBSCAN,根据地震事件的空间集中度对其进行了分类。我们确定了四个主要聚类,并利用非广延性统计物理学(NESP)的概念分析了它们的时空特性。该框架依赖于查里斯熵(Sq),描述了复杂系统的缩放行为。在此框架下,我们研究了事件间时间(T)和距离(D)分布,分别提供了 qT 和 qD熵参数。此外,我们还根据片段-不稳定性模型研究了频率-幅度分布,从而确定了非广延性参数 qM。分析结果表明,利用 NESP 可以有效地再现 Petrinja 地震序列的统计特性。此外,还估算了共震静态库仑应力变化,表明地震群的地震事件可能是由复杂断层系统的(再)激活引起的。此外,还估算了每个空间集群的有效静应力降。最后,使用超统计方法讨论了地震演变的时间模式,表明 Petrinja 地震群的时间进程受极少数自由度的控制,突出了每个地震群的时空组织。
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引用次数: 0
Reevaluating soil amplification using multi-spectral HVSR technique in La Chana Neighborhood, Granada, Spain 利用多光谱 HVSR 技术重新评估西班牙格拉纳达 La Chana 社区的土壤放大情况
IF 1.6 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2024-06-26 DOI: 10.1007/s10950-024-10227-2
Carlos Jose Araque-Perez

This work presents a thorough reevaluation of soil amplification in the La Chana neighborhood of Granada through a pioneering application of the horizontal-to-vertical spectral ratio technique on seismic noise data using various spectral approaches. The research recycles old seismic noise data recorded at 34 stations with 2 Hz instruments in the year 2010, supplemented with additional measurements recorded with broadband seismometers at nearby locations in the years 2013 and 2017. Initial traditional processing identifies a narrowband dominant frequency around 1.5 Hz, attributed to artificial or anthropogenic sources. To address this, the Maximum Entropy Algorithm was implemented to smooth the spectral response below 1 Hz, and filter out frequency peaks with very narrow spectral bands, while preserving the narrowband frequency around 1.5 Hz in some records. The Thomson Multitaper method further refined the spectral ratio, emphasizing the detection and suppression of narrow frequency bands that may be related to industrial activity. The results demonstrated the reappearance of the 1.5 Hz frequency, but this time without narrow bandwidths, indicating its possible correlation with the natural ground movement. Fundamental periods, ranging from 0.45 s to 0.88 s, suggest a diverse lithological composition, indicating the presence of layers of sands, clays, conglomerates, and carbonates over a basement that represents the main impedance contrast in the area. The multispectral approach surpasses conventional methods in precision and reliability, providing valuable insights for earthquake risk assessment, urban planning, and engineering decisions in seismically active regions.

本研究开创性地在地震噪声数据上应用了水平-垂直频谱比技术,并采用了多种频谱方法,对格拉纳达 La Chana 社区的土壤放大现象进行了全面的重新评估。这项研究回收了 2010 年在 34 个台站用 2 赫兹仪器记录的旧地震噪声数据,并补充了 2013 年和 2017 年在附近地点用宽带地震仪记录的额外测量数据。最初的传统处理方法确定了 1.5 赫兹左右的窄带主频,这归因于人工或人为源。为解决这一问题,采用了最大熵算法来平滑 1 Hz 以下的频谱响应,并滤除频谱带非常窄的频率峰,同时保留了一些记录中 1.5 Hz 附近的窄带频率。Thomson Multitaper 方法进一步完善了频谱比率,重点检测和抑制了可能与工业活动有关的窄频带。结果表明,1.5 赫兹频率再次出现,但这次没有窄频带,表明其可能与自然地面运动有关。基期从 0.45 秒到 0.88 秒不等,表明岩性成分多种多样,表明在代表该地区主要阻抗对比的基底上存在砂层、粘土层、砾岩层和碳酸盐层。多光谱方法在精确度和可靠性方面超越了传统方法,为地震活跃地区的地震风险评估、城市规划和工程决策提供了宝贵的见解。
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引用次数: 0
Directivity analysis and source parameter estimation: insights from the 2014 Arzew earthquake, Mw3.9, northwestern Algeria 指向性分析和震源参数估计:2014 年阿尔及利亚西北部阿尔泽夫 Mw3.9 地震的启示
IF 1.6 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2024-06-25 DOI: 10.1007/s10950-024-10226-3
Oualid Boulahia, Fethi Semmane

The March 20, 2014, magnitude Mw3.9 earthquake near Arzew, Algeria, instigated a study to deepen comprehension of seismic activity and hazard in the region. Analyzing data from Algerian and Spanish seismic networks, we explored earthquake characteristics and rupture mechanisms. The earthquake's epicenter was located at 35.825° latitude and -0.366° longitude, with a depth of 7 km, exhibiting intensity IV-V in the Arzew-Oran area. Preceding this event, a magnitude MD3.1 foreshock occurred on February 1, 2014, at the same location. The waveforms of the foreshock and mainshock exhibited striking similarities, validating the effectiveness of the Empirical Green's Function method employed for deconvolution. Through waveform inversion and P-wave polarities, we estimated the focal mechanism, revealing a near-pure strike-slip mechanism with nodal planes oriented ~E-W and ~N-S. The rupture process, characterized by multiple episodes, propagated predominantly from the south towards the N5°-15°E direction at a velocity around 2.7 km/s along an 870 m fault length in 0.32 seconds. The mainshock's fault plane was identified as the N-S plane, indicating the direction of rupture propagation. Source parameter estimation utilizing the EGF method revealed larger corner frequencies and stress drops compared to individual spectra estimation, attributed to the method’s improved correction for attenuation and site effects, without the need for simplified a priori models. Despite its low magnitude, the 2014 Arzew earthquake provided valuable insights into the region’s seismic behavior, contributing significantly to ground motion predictions. In particular, the study highlights the necessity of accounting for rupture directivity in seismic hazard assessments and mitigation strategies.

2014 年 3 月 20 日,阿尔及利亚阿尔泽夫附近发生了 Mw3.9 级地震,引发了一项研究,以加深对该地区地震活动和危害的理解。通过分析阿尔及利亚和西班牙地震网络的数据,我们探索了地震特征和破裂机制。这次地震的震中位于北纬 35.825°,东经-0.366°,震源深度 7 千米,在阿尔泽乌-奥兰地区表现出 IV-V 级烈度。在此次地震之前,2014 年 2 月 1 日在同一地点发生了一次 MD3.1 级前震。前震和主震的波形表现出惊人的相似性,验证了用于解卷积的经验绿色函数方法的有效性。通过波形反演和 P 波极性,我们估算了震源机制,发现这是一种近乎纯粹的走向滑动机制,节点平面的方向为 ~E-W 和 ~N-S。断裂过程以多次发作为特征,主要从南面向 N5°-15°E方向传播,速度约为 2.7 千米/秒,在 0.32 秒内沿 870 米的断层长度传播。主震的断层面被确定为 N-S 平面,表明了断裂传播的方向。与单个频谱估计相比,利用 EGF 方法进行的震源参数估计显示了更大的角频率和应力下降,这归因于该方法改进了对衰减和现场效应的校正,而无需简化先验模型。尽管震级较低,但 2014 年阿尔泽夫地震为该地区的地震行为提供了宝贵的见解,对地动预测做出了重大贡献。特别是,该研究强调了在地震灾害评估和减灾战略中考虑破裂指向性的必要性。
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引用次数: 0
Earthquake detection capacity of the Dense Oceanfloor Network system for Earthquakes and Tsunamis (DONET) 地震和海啸密集洋底网络系统(DONET)的地震探测能力
IF 1.6 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2024-06-06 DOI: 10.1007/s10950-024-10219-2
K. Z. Nanjo, Y. Yamamoto, K. Ariyoshi, H. Horikawa, S. Yada, N. Takahashi

We studied the earthquake detection capacity of DONET (Dense Oceanfloor Network system for Earthquakes and Tsunamis) operating in the Nankai Trough, a target region monitored for future megathrust earthquakes. The focus of this paper was to evaluate the impact on this capacity from the malfunction of parts of the network. For this purpose, the completeness magnitude, above which all earthquakes are considered to be detected by a seismic network, was used. Then, a catalog that includes events observed by DONET was used. We found spatiotemporal variability of completeness magnitude, ranging from values below 1 in one of the areas where stations are densely deployed to values above 2 at the periphery and outside of the DONET area. We conducted a simulation computation for cases of malfunction of densely distributed stations. The results showed that completeness estimates in the area near the malfunctioning stations were about 1 magnitude larger. This implies that malfunction repair and/or replacement with new stations would be desirable because they pronouncedly affect earthquake monitoring. We then demonstrated an example of how to use the information of completeness magnitude as prior knowledge to compute the b value of the Gutenberg-Richter distribution. The result indicates the b value as a proxy that can help to image stress heterogeneity when there is a magnitude-6 class slow slip event on the Nankai Trough plate boundary.

我们研究了在南海海槽运行的 DONET(地震和海啸密集洋底网络系统)的地震探测能力,南海海槽是未来特大地壳地震的监测目标区域。本文的重点是评估部分网络故障对这一能力的影响。为此,本文使用了完整性量级,即地震台网检测到的所有地震均超过该量级。然后,使用包含 DONET 观测到的事件的目录。我们发现完整度的时空变化很大,从密集布设台站的一个地区的低于 1 到 DONET 区域外围的高于 2 不等。我们对密集布设的台站出现故障的情况进行了模拟计算。结果表明,故障台站附近区域的完整性估计值要高出约 1 个量级。这意味着故障修复和/或更换新台站是可取的,因为它们会明显影响地震监测。然后,我们举例说明了如何利用完好性震级信息作为先验知识来计算古腾堡-里克特分布的 b 值。结果表明,当南海海槽板块边界发生 6 级慢速滑动事件时,b 值作为一种替代值可帮助映射应力异质性。
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引用次数: 0
Significance of VP/VS ratio in locating earthquakes of a long-duration swarm in the western coast of India VP/VS 比率在印度西海岸长持续时间地震群定位中的意义
IF 1.6 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2024-06-05 DOI: 10.1007/s10950-024-10223-6
Himangshu Paul, T. C. Sunilkumar, Vineet K. Gahalaut, D. Srinagesh, M. Shekar

The earthquake swarm in Palghar, western India, is a natural laboratory to understand long-duration seismogenesis. However, it requires an accurate estimation of the key parameters, such as earthquake locations and the velocity model of the region. Two separate studies performed by two organisations in India, the CSIR-National Geophysical Research Institute (NGRI) and the National Center for Seismology (NCS) reported significantly differing results from the first 8–12 months of earthquake monitoring in Palghar. CSIR-NGRI reported the depth of earthquakes in the range of 4–15 km, whereas NCS reported a much shallower depth down to 7 km only. We investigate the reason for this depth discrepancy by analysing datasets from the networks of both these organisations. We find that no available velocity models are able to reconcile the depth difference between the two datasets. Selection criteria generally adopted to determine a good velocity model, such as travel-time residuals and location errors, also failed to identify a suitable velocity model. Several synthetic tests helped us to identify that the network geometry and source-station separation are contributing factors to the observed depth difference. However, the main reason for the discrepancy was found to be inconsistent velocity models used for location at both networks. The main objective of our work is to estimate a velocity model which minimises the depth discrepancy between both datasets. In this regard, we synthetically generated hundreds of models with different VP and VP/VS ratios, followed by a grid search of VP and VP/VS ratios, which harmonises the location from the two datasets. The best model consists of a VP lying between 5.55–5.85 km/s and a VP/VS ratio between 1.77–1.81. For this velocity model, there is a greater overlap of the hypocentral clouds from both networks, and about 80% of the earthquakes of the CSIR-NGRI network were located within depths ≤ 7 km. We find that location errors vary seasonally, which is also related to the VP/VS of the crust. Since earlier studies have also found a strong correspondence between rainfall and seismicity in this region, we infer that the high VP/VS ratio might have been caused by the rainfall saturation of cracks in the Palghar seismicity zone.

印度西部帕尔加尔的地震群是了解长时间地震发生的天然实验室。然而,这需要对地震位置和该地区的速度模型等关键参数进行精确估算。印度的两家机构--CSIR-国家地球物理研究所(NGRI)和国家地震学中心(NCS)--分别进行了两项研究,报告了帕尔加尔最初 8-12 个月的地震监测结果,但结果大相径庭。CSIR-NGRI 报告的地震深度在 4-15 千米之间,而 NCS 报告的地震深度要浅得多,只有 7 千米。我们通过分析这两个组织网络的数据集,研究了造成这种深度差异的原因。我们发现,现有的速度模型都无法调和两个数据集之间的深度差异。一般用于确定良好速度模型的选择标准,如行进时间残差和位置误差,也未能确定合适的速度模型。几项合成测试帮助我们确定了网络几何形状和源站分离是造成观测到的深度差异的因素。然而,我们发现造成差异的主要原因是两个网络用于定位的速度模型不一致。我们工作的主要目标是估算一个速度模型,使两个数据集之间的深度差异最小。为此,我们合成了数百个具有不同 VP 和 VP/VS 比率的模型,然后对 VP 和 VP/VS 比率进行网格搜索,从而协调了两个数据集的定位。最佳模型是 VP 介于 5.55-5.85 km/s 之间,VP/VS 比值介于 1.77-1.81 之间。对于这个速度模型,两个网络的低中心云有更大的重叠,CSIR-NGRI 网络约 80% 的地震都位于深度 ≤ 7 km 的范围内。我们发现定位误差随季节变化,这也与地壳的 VP/VS 有关。由于早先的研究也发现该地区的降雨量与地震发生率之间存在很强的对应关系,我们推断 VP/VS 比率高可能是由于帕尔加尔地震带裂缝的降雨饱和造成的。
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引用次数: 0
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Journal of Seismology
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