TSVD analysis of Euler deconvolution to improve estimating magnetic source parameters: An example from the Åsele area,Sweden

In this paper, I introduce a new approach based on truncated singular value decomposition (TSVD) analysis for improving implementation of grid-based Euler deconvolution with constraints of quasi 2D magnetic sources. I will show that by using TSVD analysis of the gradient matrix of magnetic field anomaly (reduced to pole) for data points located within a square window centered at the maximum of the analytic signal amplitude, we are able to estimate the strike direction and dip angle of 2D structures from the acquired eigenvectors. It is also shown that implementation of the standard grid-based Euler deconvolution can be considerably improved by solving the Euler's homogeneity equation for source location and structural index, simultaneously, using the TSVD method. The dimensionality of the magnetic anomalies can be indicated from the ratio between the smallest and intermediate eigenvalues acquired from the TSVD analysis of the gradient matrix. For 2D magnetic sources, the uncertainty of the estimated source location and structural index is significantly reduced by truncating the smallest eigenvalue.Application of the method is demonstrated on an aeromagnetic data set from the Åsele area in Sweden. The geology of this area is dominated by several dike swarms. For these dolerite dikes, the introduced method has provided useful information of strike directions and dip angles in addition to the estimated source location and structural index.     

Seismic tomography and anisotropy in the source area of the 2008 Iwate–Miyagi earthquake (M 7.2)

In order to understand the generation mechanism of the Iwate–Miyagi earthquake (M 7.2) that occurred on 14 June 2008 in Northeast Japan, we determined high-resolution 3D seismic velocity (Vp, Vs) and Poisson's ratio (σ) structures as well as P-wave azimuthal anisotropy in and around the source area using 246,623 P-wave and 189,153 S-wave high-quality arrival times from 1941 aftershocks of the 2008 Iwate–Miyagi earthquake as well as 4878 shallow and intermediate-depth earthquakes in this area recorded by the dense High-Sensitivity Seismic Network (Hi-net) and the seismic stations of Tohoku University. Our results show that hypocenters of the mainshock and three large aftershocks are located in a boundary zone where both seismic velocity and Poisson's ratio change drastically in a short distance. A zone with pronounced low-velocity and high Poisson's ratio is revealed in the lower crust and uppermost mantle under the source area, which may reflect the arc magma and fluids ascending from the upper-mantle wedge. The P-wave azimuthal anisotropy is complex under the study area, which may also indicate the complex crustal structure there. These results indicate that the generation of the 2008 Iwate–Miyagi earthquake was influenced by the ascending arc magma and fluids associated with the dehydration reactions of the subducting Pacific slab under Northeast Japan.     

Following the curve? Reviewing the physical basis of the SCS curve number method for estimating storm runoff

Less attention has been paid to runoff generation from semi-arid than from humid-temperate catchments. The SCS curve number approach is simple to apply and widely used, but lacks physical underpinning. Here output from a runoff generation models is compared with data from field measurements, making use of 11 years data from rainfall and runoff events at the Sierra de Enguera Soil Erosion Experimental Station in Eastern Spain. Runoff from natural rainfall events was monitored for 10 years on bare plots of 1–16 m length. The largest storm event was of 142 mm, generating runoff of up to 115 mm on the smallest plots. The model presented simulates overland storm flow on a sloping rough and unvegetated surface, representing an area of 320 × 320 m. Green-Ampt infiltration constants are randomly assigned to each cell in a 128 × 128 grid, and rectangular storms applied at a range of total amounts and intensities to simulate runoff at each transect across the area. A simple algebraic expression is developed to estimate total runoff and storage in terms of storm size and duration, and plot length, with parameters that reflect infiltration behaviour, and this expression is compared with the SCS curve number approach. For the very largest storms, both expressions converge asymptotically towards 100% runoff, but the revised expression greatly improves estimates of runoff from smaller events. Output of these simulations is compared with measured storm runoff data on bare runoff plots at the Sierra de Enguera experimental Station in SE Spain and gives further support to the proposed expression for storm runoff.     

Earthquake magnitude estimation using the τc and Pd method for earthquake early warning systems

Earthquake early warning （EEW） systems are one of the most effective ways to reduce earthquake disaster. Earthquake magnitude estimation is one of the most important and also the most difficult parts of the entire EEW system. In this paper, based on 142 earthquake events and 253 seismic records that were recorded by the KiK-net in Japan, and aftershocks of the large Wenchuan earthquake in Sichuan, we obtained earthquake magnitude estimation relationships using the τe and Pa methods. The standard variances of magnitude calculation of these two formulas are ±0.65 and ±0.56, respectively. The Pd value can also be used to estimate the peak ground motion of velocity, then warning information can be released to the public rapidly, according to the estimation results. In order to insure the stability and reliability of magnitude estimation results, we propose a compatibility test according to the natures of these two parameters. The reliability of the early warning information is significantly improved though this test.     

Effects of site stiffness and source to receiver distance on surface wave tests׳ results

By using six 4.5 Hz geophones, surface wave tests were performed on four different sites by dropping freely a 65 kg mass from a height of 5 m. The receivers were kept far away from the source to eliminate the arrival of body waves. Three different sources to nearest receiver distances (S), namely, 46 m, 56 m and 66 m, were chosen. Dispersion curves were drawn for all the sites. The maximum wavelength (λ_max), the maximum depth (d_max) up to which exploration can be made and the frequency content of the signals depends on the site stiffness and the value of S. A stiffer site yields greater values of λ_max and d_max. For stiffer sites, an increase in S leads to an increase in λ_max. The predominant time durations of the signals increase from stiffer to softer sites. An inverse analysis was also performed based on the stiffness matrix approach in conjunction with the maximum vertical flexibility coefficient of ground surface to establish the governing mode of excitation. For the Site 2, the results from the surface wave tests were found to compare reasonably well with that determined on the basis of cross boreholes seismic tests.     

Earthquake magnitude estimation using the τ c and P d method for earthquake early warning systems

Earthquake early warning (EEW) systems are one of the most effective ways to reduce earthquake disaster. Earthquake magnitude estimation is one of the most important and also the most difficult parts of the entire EEW system. In this paper, based on 142 earthquake events and 253 seismic records that were recorded by the KiK-net in Japan, and aftershocks of the large Wenchuan earthquake in Sichuan, we obtained earthquake magnitude estimation relationships using the τ _c and P _d methods. The standard variances of magnitude calculation of these two formulas are ±0.65 and ±0.56, respectively. The P _d value can also be used to estimate the peak ground motion of velocity, then warning information can be released to the public rapidly, according to the estimation results. In order to insure the stability and reliability of magnitude estimation results, we propose a compatibility test according to the natures of these two parameters. The reliability of the early warning information is significantly improved though this test.     

Moment tensor inversion and source rupture process of the September 27, 2003 M_S=7.9 earthquake occurred in the border area of China, Russia and Mongolia

IntroductionOn September 27, 2003, an earthquake of MS=7.9 struck the border area of China, Russia and Mongolia. According to the field investigation from the Earthquake Administration of XinjiangAutonomous Region, the whole northern Tianshan region felt the hit. Buildings and structures within six counties and one city in Altay region, which is total about 0.11×106 km2 area, were damaged to different extent and caused certain economic losses. The epicenter determined by China National …     

Comparison and analysis of the stress field in the source region of Tangshan and Lancang earthquake sequences

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In search of potential earthquake source regions in the Chinese mainland in the light of ambient shear stress field

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3-D velocity images of the crust and upper mantle of the Tianshan area

（胥颐，朱介寿，刘志坚，张华卿，朱燕）３－ＤｖｅｌｏｃｉｔｙｉｍａｇｅｓｏｆｔｈｅｃｒｕｓｔａｎｄｕｐｐｅｒｍａｎｔｌｅｏｆｔｈｅＴｉａｎｓｈａｎａｒｅａ￥ＹｉＸＵ；Ｊｉｅ－ＳｈｏｕＺＨＵ；Ｚｈｉ－ＪｉａｎＬＩＵ；Ｈｕａ－ＱｉｎｇＺＨＡＮＧａｎｄＹａ...     

An updated method for estimating landslide‐event magnitude

Summary statistics derived from the frequency–area distribution (FAD) of inventories of triggered landslides allows for direct comparison of landslides triggered by one event (e.g. earthquake, rainstorm) with another. Such comparisons are vital to understand links between the landslide‐event and the environmental characteristics of the area affected. This could lead to methods for rapid estimation of landslide‐event magnitude, which in turn could lead to estimates of the total triggered landslide area. Previous studies proposed that the FAD of landslides follows an inverse power‐law, which provides the basis to model the size distribution of landslides and to estimate landslide‐event magnitude (mLS), which quantifies the severity of the event. In this study, we use a much larger collection of earthquake‐induced landslide (EQIL) inventories (n=45) than previous studies to show that size distributions are much more variable than previously assumed. We present an updated model and propose a method for estimating mLS and its uncertainty that better fits the observations and is more reproducible, robust, and consistent than existing methods. We validate our model by computing mLS for all of the inventories in our dataset and comparing that with the total landslide areas of the inventories. We show that our method is able to estimate the total landslide area of the events in this larger inventory dataset more successfully than the existing methods. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

潜在震源区震级上限不确定性研究

潜在震源区的震级上限（Mu）是指在该潜在震源区内可能发生的最大地震的震级．预期未来发生超过该震级地震的概率趋于0．本文运用误差分析及逻辑树等方法,并结合发震模型的数值模拟得到的大震合成目录等结果,系统分析并最终得到了不同途径给出的不同类型潜在震源区震级上限的不确定性．该结果可直接应用于包括地震区划在内的工程地震以及活动断裂危险性评价等工作中．     

震级离散下的震级频度关系

运用最大熵原理,研究震级离散条件下震级频度关系,得到震级离散条件下震级概率分布函数,结果表明:(1)震级大于等于某一震级的地震次数应通过离散求和的方式得到,而不应通过积分的方式得到;(2) 震级上限取为∞的情况下,古登堡意义和里克特意义两种震级频度关系式的b值相等;震级上限有限的情况下,里克特意义震级频度关系式可能不是直线.     

Revision of the amplitude-distance relation for local magnitude estimation in Italy

Maximum amplitude observations of local and regional seismic phases(S _g and L _g, with 800 km) recorded by stations of the I.N.G.National Seismological Network in the period 1994–1999 have beenused to investigate the attenuation of such phases in Italy. The propagationmodel adopted herein accounts for both geometrical spreading, with a termdepending on a given power of distance, and inelastic absorption of themedium, with a term depending exponentially on the distance. Fitting theparameters of the model with experimental data, we considered two cases:assuming a quality factor Q proportional to the frequency f orindependent of f. We compared our results with the values tabled byRichter in 1935, which are still used for the local magnitude estimate in theI.N.G. bulletins. The values found in this study are different than thosegiven by Richter. This suggests that these new values should be used insteadto compute the local magnitude in Italy.     

川滇地区强余震的震级分布和距离分布特征

研究了川滇地区1966年以来12次主震震级MSge;6.5的地震序列中,主震与强余震（本文定义为所有MSge;5的余震）震级差分布特征和强余震与主震距离的分布特征. 结果表明,强余震与主震震级差服从截断的指数分布,据此推导出了强余震与主震震级差的概率密度函数; 强余震距离分布的优势范围是距主震10——39 km,且强余震与主震震中的距离服从正态分布.      

分区量规函数在河北地震台网近震震级测定的适用性

选取河北地震台网2008—2016年记录的1 714个M_L≥0.1地震,采用分区量规函数（新量规函数）重新计算并对比分析M_L震级。实际结果表明,采用新旧量规函数计算得到的近震震级一致性较好,M_L震级偏差在±0.1的地震共1 556个,约91.8%,且抽样地震近震震级均值和标准方差更小。因此,使用分区量规函数,河北地震台网近震震级测定精度和适用性更好。     

东南沿海地震带的地震丛集窗及震级结构特征分析

基于东南沿海地震带的地震活动特点和构造背景, 确定了若干个地震活动特别集中的区域, 并引入地震丛集窗和震级结构的概念分析这些区域的局部特点。结果表明, 这些地震丛集窗的地震活动水平变化反映了所属大区的应力状态, 当某个地震丛集窗发生震级结构异常, 具备前兆震群特征的地震密集事件时, 该地震丛集窗内或其相关部位的介质性状可能发生了变化, 这对以后可能对应发生中强地震或强震具有一定的中期预测效能。     

川滇地区烈度计台站测定震级校正分析

烈度计台与测震台的布设环境、仪器类型不同,所测定的震级值存在一定差异。收集2017—2019年川滇地区301个烈度计台站记录的46次M_L 3.0以上地震,进行震级校正。统计烈度计实测震级值与测震台网平均震级值的偏差,对原量规函数进行修正,进而做台站校正。综合修正后,利用量规函数和台站校正值重新计算烈度计震级,结果表明:在震中100 km范围内,烈度计测定震级偏差平均值由校正前的0.145降低至0.033,标准差由0.382降低至0.295,离散度减小;校正后的烈度计震级结果较优,说明本研究获得的量规函数和台站校正值更加适用于川滇地区烈度计台站的震级计算。     

昆明数字遥测台网近震震级的测定

2000年1月至2002年8月昆明数字遥测台网26个子台记录的718个地震的数字地震记录,通过系统的传递函数,仿真为短周期的DD-1地动位移记录和中长周期DK-1的地动速度记录,记录仿真前后均测定地震震级,分别记为Msz和Mfz;对其中云南常规模拟地震台网40个台站记录的259个地震,也从记录图纸测定了地震震级,记为Mmn。对Mfz、Msz和Mmn进行系统的比较表明:在1.0≤ML<2.5的地震中,仿真后所测震级Mfz比仿真前所测震级Msz平均偏高0.16;在2.5≤ML≤2.9的地震中,Mfz比Msz平均偏高0.12;而在3.0≤ML≤3.9的地震中,Mfz与Msz的平均偏差基本为0;ML≥4.0的地震中,Mfz比Msz平均偏小0.02;MS的仿真震级Mfz比Msz平均偏高0.04;特别由模拟记录所测的震级Mmn与Mfz的平均偏差基本为0;不同震级间的差别基本呈正态分布。     

Dependence of correlations between spectral accelerations at multiple periods on magnitude and distance

In this paper, the dependence of correlations between spectral accelerations at multiple periods on magnitude (M) and distance (R) has been investigated. For this purpose, a relatively large dataset of ground motion records (GMRs), containing 1551 records with a wide range of seismic characteristics, was selected. It is shown that the difference in the correlation coefficient is statistically meaningful when the general GMR dataset is divided into two subsets based on an arbitrary M or R. The observed difference is more meaningful in the case of magnitude when compared with distance. The general dataset of GMRs was then divided into four separate subsets based on optimum values of M and R, so that the four obtained subsets were given the greatest dissimilarity in terms of the correlation coefficients. The correlation coefficients between spectral accelerations at multiple periods were calculated in the case of the four subsets and compared with the available correlations in the literature. The conditional mean spectrum was also calculated by means of the conventional correlation coefficients, as well as by using the proposed M and R dependent correlation coefficients. The results show that, despite the commonly available findings in the literature, this dependence is significant and should not be neglected in the conditional spectra calculation process. Copyright © 2013 John Wiley & Sons, Ltd.