Layered Velocity Models of the Western Bohemia Region

A new robust and effective optimization algorithm – isometric algorithm – was used for the inversion of layered velocity models, with constant gradient in each layer, to find suitable 1-D models for the location of microearthquakes in the individual four subregions of the West Bohemian earthquake swarm region. Models which are considered as optimal yield the minimum sum of the absolute values of the travel-time residua in locating the whole group of earthquakes in the given subregion. The results obtained from the inversion of P and S waves and from P waves only are shown. For comparison, optimum homogeneous models derived by the grid search method, again using both P and S waves and P waves only, are given. The computations indicate that the models for the individual subregions differ from each other. For layered models the differences are more pronounced, as expected, in the upper parts, down to depths of about 5 km. In comparison with the subregions Nový Kostel and Plesná, the P and S wave velocities for subregion Lazy are relatively higher and the P and S velocities for subregion Klingenthal relatively lower. In the lower parts the differences are smaller and the velocities have practically identical gradients. The highest velocities were obtained for subregion Lazy and the lowest velocities for subregion Klingenthal, as well for the homogeneous models. The model that represents the whole swarm region was determined in a similar way. This model is compared with the previously published velocity-depth distribution, obtained from DSS profile VI/70 in the vicinity of the area under study.     

2022年10月—2023年2月中国大陆地区M≥4.0地震震源机制解测定

利用中国地震台网记录的宽频带波形资料,采用近震全波形反演方法得到2022年10月1日—2023年2月28日发生在中国大陆地区的M≥4.0共46次地震的震源机制解以及2023年1月30日新疆沙雅M6.1地震的矩心位置和矩心偏移时间。结果显示逆断型15次,走滑型15次,正断型14次,未知型2次。     

2022年7—9月中国大陆地区M≥4.0地震震源机制解测定

利用中国地震台网记录的宽频带波形资料,采用近震全波形反演方法得到2022年7月1日—9月30日发生在中国大陆地区的M≥4.0共18次地震的震源机制解以及2022年9月5日四川泸定M6.8地震的矩心位置和矩心偏移时间。结果显示逆断型6次,走滑型7次,正断型4次,未知型1次。      

岷县M_S6.6地震震源机制及构造应力研究

利用甘肃省测震台网观测到的主震波形记录的初动符号求解了2013年7月22 日岷县Ms6.6地震主震的震源机制,并与哈佛及usgs发布的震源机制进行了对比,对这一地区过去发生过的若干次Mb4.5以上的地震也利用初动符号求解了震源机制,发现与Ms6.6地震的震源机制形态较为相似.进而利用2010年至2011年甘东南宽频带流动台阵的大量近震资料,对在震中距50 km范围内,并且接近岷县Ms6.6地震发震断裂临潭-宕昌断裂的中小地震进行了检索,对检索到的地震进行初动识别后得到初动数目大于10个、并且对震源包络良好的中小地震31个,利用小震的震源机制解求解了该区域的区域应力场.结果表明这一区域的主压力方向为NEE方向.     

日本东北MW9.0地震的PI模型参数设置与预测效能回溯性检验

以日本局部地区（32.0°N—46.0°N,136.0°E—148.0°E）为研究区域,应用图像信息（PI）方法,获得了不同计算参数模型下包含2011年3月11日日本东北M_W9.0地震的多组预测窗热点图像。以0.5°×0.5°和1.0°×1.0°的网格尺度和5—10年预测窗长为主要参数变量,并以R值和受试者工作特征（ROC）方法检验不同参数模型下PI方法的预测效能。结果表明,多组参数模型下M_W9.0地震所在预测窗内,其震中所在网格及其摩尔邻近网格均曾出现热点图像,表明PI方法可对日本东北M_W9.0地震作出预测。综合R值评分和ROC检验分析可知,网格尺度相对较大、预测窗长相对较长的模型,其预测效果更好。      

Location and moment tensor inversion of small earthquakes using 3D Green’s functions in models with rugged topography: application to the Longmenshan fault zone

With dense seismic arrays and advanced imaging methods, regional three-dimensional(3D) Earth models have become more accurate. It is now increasingly feasible and advantageous to use a 3D Earth model to better locate earthquakes and invert their source mechanisms by fitting synthetics to observed waveforms. In this study, we develop an approach to determine both the earthquake location and source mechanism from waveform information. The observed waveforms are filtered in different frequency bands and separated into windows for the individual phases. Instead of picking the arrival times, the traveltime differences are measured by cross-correlation between synthetic waveforms based on the 3D Earth model and observed waveforms. The earthquake location is determined by minimizing the cross-correlation traveltime differences. We then fix the horizontal location of the earthquake and perform a grid search in depth to determine the source mechanism at each point by fitting the synthetic and observed waveforms. This new method is verified by a synthetic test with noise added to the synthetic waveforms and a realistic station distribution. We apply this method to a series of M_W3.4–5.6 earthquakes in the Longmenshan fault(LMSF) zone, a region with rugged topography between the eastern margin of the Tibetan plateau and the western part of the Sichuan basin. The results show that our solutions result in improved waveform fits compared to the source parameters from the catalogs we used and the location can be better constrained than the amplitude-only approach. Furthermore, the source solutions with realistic topography provide a better fit to the observed waveforms than those without the topography, indicating the need to take the topography into account in regions with rugged topography.     

青藏高原东北隅弧形构造区现代中小地震密集区与历史强震的关系探讨

青藏高原东北隅地区位于青藏高原、鄂尔多斯和阿拉善三大块体交汇部位,发育一组以逆走滑活动为主的弧形断裂系,其新活动性强,历史及现代强震频发,是探讨现代中小地震密集区与历史强震关联性的理想地区,也是检验和发展小震密集区值方法及其适用条件的有利地区.本文采用甘肃省地震局对该区1970年以来1～5级地震仪器监测目录,利用网格点...     

Anomaly of the ionospheric electron density close to earthquakes: Case studies of Pu'er and Wenchuan earthquakes

The electron density recorded onboard the DEMETER satellite was analyzed to search for possible anomalies before earthquakes both in space and time. To distinguish pre-earthquake anomalies from the other anomalies related to geomagnetic activity, data were filtered using the K_p index. The analysis is based on the comparison of data recorded closely to earthquakes in space and time and past data for the same area. In analyzing data around the time and location of the Pu’er and Wenchuan earthquakes, obvious anomalies in electron density were found close to the epicenters, and some remarkable disturbances were detected before the earthquakes occurred. The results were finally compared with those of previous works that used the same data but employed different analysis methods. Good agreement was found which suggests that these anomalies have a close relation to the earthquake preparation.     

大震前区域地震活动应变场的时空异常特征

本文基于自然正交函数展开方法, 以地震应变为变量, 计算1980年以来中国大陆7级以上大震前的地震应变, 提取出大震前区域地震活动应变场的时空异常。 结果表明大震前时间因子在平稳背景上会出现突跳上升或突跳下降异常变化。 一般情况下, 前4个应变场中至少有3个出现异常变化, 异常分布具有多分量特点, 出现的最早时间大约在震前3年, 少数出现在震前1~6个月。 对比应变场时间因子异常与研究区域每个网格单元(0.5°×0.5°)内的地震能量时间因子异常形态的相似性、 时间的一致性, 找出地震应变场空间异常位置。 结果表明, 多数大震前的空间异常分布在主震震中周围; 少数大震的空间异常远离主震震中。 产生这种现象的原因是大震前与主震不同距离的单元网格内发生中短期或者临震的震群、 显著地震等地震活动性异常。     

强震作用下不同处理方式黄土地基抗震陷性能评价

由于黄土高原区抗震设防标准长期偏低,无法承受强震带来的严重灾害链后果,因此为了提高地基及公路路基的抗强震能力,以强震动荷载为试验输入条件,以强夯、粉煤灰、水泥土等三种地基改性处理试样为研究对象,对其进行室内动三轴试验,寻找针对震陷性黄土工程场地更加经济、科学的抗震陷地基处理方法,研究不同地基改性处理方法在强震动荷载下的残余应变特性,得到强震作用与残余应变的定量关系,并从变形特征和动载振次两个角度对比三类方法的适用性。在此基础上,估算场地不同地基处理方式下的震陷量,给出强震荷载下不同工程场地有效的抗震陷处理方法与评价办法,为黄土场地抗震设计和地基处理提供参考依据。     

HYPO2000与单纯形定位方法对比及作为速报算法的可行性分析

选取福建、陕西的12次爆破事件,安徽测震台网的6次速报地震事件以及4次地震台站出现GPS时钟错误的地震事件,运用两种地震定位方法进行定位。结果表明：对于网内地震,HYPO2000程序稍优于单纯形定位结果;对于网缘及网外地震,单纯形优于HYPO2000程序的定位结果。     

晋冀蒙交界地区地震危险性评估及地震活动性分析

本文利用晋冀蒙交界地区1500年以来记录较完整的M_S5.0及以上历史地震烈度资料和2000年以来的地震活动资料，分别进行地震灾害危险性和地震活动性分析。首先，利用ArcGIS将历史地震烈度资料数字化，没有等震线记录的地震用烈度衰减关系计算烈度圈半径。将研究区划分成0.1°×0.1°的网格，将烈度资料分配到与之相交的每个网格，并用烈度-频度关系计算每个网格的烈度a、b值。基于地震发生遵从泊松分布的假定，估算未来50年内晋冀蒙交界区遭受某一地震烈度的超越概率。同时，计算50年超越概率10%对应的地震烈度，计算结果表明张家口蔚县、阳原和山西广灵县周边地区的地震危险性较高。最后，采用中小地震能量密度值计算方法，对2000年以来的现今地震活动进行定量分析，与历史地震烈度资料分析结果进行对比，发现中小地震活动圈定的危险区与历史地震烈度资料评估计算的概率高值区相对应，因此，这两种方法可为晋冀蒙交界地区的地震活动性和危险性评价提供参考。     

Calibration of the Tibetan Plateau Using Regional Seismic Waveforms

We use the recordings from 51 earthquakes produced by a PASSCAL deployment in Tibet to develop a two-layer crustal model for the region. Starting with their ISC locations, we iteratively fit the P-arrival times to relocate the earthquakes and estimate mantle and crustal seismic parameters. An average crustal P velocity of 6.2–6.3 km/s is obtained for a crustal thickness of 65 km while the P velocity of the uppermost mantle is 8.1 km/s. The upper layer of the model is further fine-tuned by obtaining the best synthetic SH waveform match to an observed waveform for a well-located event. Green's functions from this model are then used to estimate the source parameters for those events using a grid search procedure. Average event relocation relative to the ISC locations, excluding two poorly located earthquakes, is 16 km. All but one earthquake are determined by the waveform inversion to be at depths between 5 and 15 km. This is 15 km shallower, on average, than depths reported by the ISC. The shallow seismicity cut-off depth and low crustal velocities suggest high temperatures in the lower crust. Thrust faulting source mechanisms dominate at the margins of the plateau. Within the plateau, at locations with surface elevations less than 5 km, source mechanisms are a mixture of strike-slip and thrust. Most events occurring in the high plateau where elevations are above 5 km show normal faulting. This indicates that a large portion of the plateau is under EW extension.     

黄土边坡动力响应分析

运用有限差分软件FLAC3D,建立了某一黄土边坡三维模型,首先对其在地震作用下的动力响应规律进行了总结,然后探讨了地震动参数对黄土边坡动力响应的影响。结果表明：黄土边坡对地震波存在垂直放大和临空面放大作用;当输入地震波振幅或频率增加时,坡面监测点加速度放大系数随坡高增加呈＂增加→衰减→增加＂的三段形态;速度放大系数随坡高的增大而增大,并在坡顶达到最大值;位移放大系数随振幅和频率的增加而增加;地震持时对加速度、速度峰值的影响不大,但坡体位移随持时的增加而显著增加。强震作用下的最大剪应变增量区域的位置和形状表明,黄土边坡的破坏模式仍是沿着某一弧形潜在滑动面失稳破坏。研究结果有助于进一步揭示黄土边坡在地震作用下的失稳机制,为黄土地区边坡抗震设计与防灾减灾提供参考。     

区域一维速度模型对地震定位的定量影响

利用2017年8月1日至2017年12月31日四川地震台网和甘肃地震台网记录到的发生在青藏高原东缘的731个地震事件的9 284条Pg震相到时数据,首先反演了该地区的“最小一维速度模型”,并将该模型和选取的速度模型建立对比模型,以九寨沟地震序列为研究目标,定量讨论了两种速度模型分别在绝对定位和相对定位方法中对定位结果的影响。所得定位结果表明:反演获得的“最小一维速度模型”在重定位中可以有效地减小地震走时均方根残差;绝对定位比相对定位更加依赖于一维速度模型,一维速度模型会直接影响绝对定位结果中的震源分布形态,但在相对定位结果中仅起到调整地震事件相对位置的作用;在地震绝对定位中,震级越大的地震对于速度模型越敏感,而这一特点在相对定位中表现得并不明显。通过本项研究可知,在地震定位研究中,联合采用绝对定位和相对定位方法是最佳策略。      

Probability of earthquake recurrence with nonuniform stress rates and time-dependent failure

Current methods for calculation of long-term probabilities for the recurrence of large earthquakes on specific fault segments are based upon models of the faulting process that implicitly assume constant stress rates during the interval separating earthquakes and instantaneous failure at a critical stress threshold. However, observations indicate that the process of stress recovery following an earthquake involves rate variations at all time scales in addition to stress steps caused by nearby earthquakes. Additionally, the existence of foreshocks, aftershocks and possible precursory processes suggest that there may be significant time dependence of the earthquake nucleation process. A method for determining the conditional probabilities for earthquake occurrence under conditions of irregular stressing is developed that could be useful at all time scales including those pertinent to short-and intermediate-term prediction. Used with models for earthquake occurrence at a stress threshold, the addition of variable stressing introduces a simple scaling of the conditional probabilities by stress level and stress rate. A model for the time-dependent nucleation of earthquake slip has been proposed recently that is based upon laboratory observations of fault strength. This failure criterion results in large but relatively short duration changes in the probability of earthquake recurrence particularly following stress steps. Applied to populations of earthquakes the models predicts a 1/t decay of seismicity following stress steps as observed for aftershocks and for frequency of foreshock-mainshock pairs. The model suggests that variations of seismicity rates of small earthquakes in the nucleation zone of the expected earthquake directly indicate variations in probability of recurrence of the large earthquake.     

复杂速度模型的地震交切定位方法

交切法是最基本的地震定位方法之一,该定位方法具有稳定性强、速度快的优点。由于速度模型假设为均匀或水平均匀介质,与实际介质有较大偏差,因此定位精度较低,特别是震源深度。为克服传统交切法的缺点,我们对其进行了改进。在改进的方法中,震源轨迹不再假设为圆形或双曲线形,而是利用最小走时树射线追踪方法进行精确计算。数值模型计算表明,本文提出的改进方法,可用于复杂速度模型的地震定位。     

三维复杂速度模型的交切法地震定位

地震定位是地震监测与减灾研究重要基础.基于均匀或横向均匀介质模型,利用震源轨迹确定震源位置的交切法具有稳健和效率高的优点,但定位精度较低,特别是震源深度.为提高震源定位精度,我们提出适用于三维复杂速度模型的地震定位交切法.将地壳速度模型由均匀或横向均匀介质模型扩展为三维复杂速度模型;均匀或横向均匀介质模型对应的原假设为球面或双曲面的震源轨迹通过最小走时树射线追踪技术予以确定.确定震源位置的震源轨迹以到时差作为约束条件;将震源定位于震源轨迹交汇最密集的点处,即总的到时差残差(RDT)最小的点处.定位结果的不确定性可通过RDT值较小节点的空间分布予以定性表示.考察了准确速度模型、扰动速度模型、扰动观测到时及地震在台网外等4种情况下改进方法的地震定位效果,结果表明改进的交切法可用于三维复杂速度模型的地震定位;综合利用P波与S波的到时差信息,可明显改善震源位置约束;使用多条震源轨迹进行定位,有助于减少由随机因素导致的定位误差.     

线性单事件地震定位方法的改进及应用尝试

根据大震速报和快速预警实际需要,首先对Inglada线性单事件定位方法进行了适当的改进, 使其在仅有P波到时数据的情况下也能快速定位,且求解过程仅需简单迭代而不用奇异值分解; 其次, 尝试将改进后的方法从单层均匀模型引入到分层均匀模型中的近源台网定位情形,并通过单层均匀和分层均匀两种不同模型的理论实验讨论了该方法的可行性和适用范围; 最后整合了质量高且分布较好的距离2008年汶川M_S8.0地震震中最近的强震、微震, 以及川西流动台阵等观测记录资料,对汶川M_S8.0主震初始破裂点的时空参数进行了多种模型的定位实验. 结果表明, 改进后的线性单事件定位方法简单、快捷、易用,可广泛应用于近源地震定位,尤其是用于无法得到S波到时的中强以上直至巨大地震的速报、地震现场流动台网的快速定位以及地震的快速预警等.      

sPL震相在九江—瑞昌M_S5.7地震序列震源深度测定中的应用

利用近震深度震相sPL的基本特征和九江地震台的波形资料,对2005年11月26日九江—瑞昌MS5.7地震序列ML2.0地震进行了sPL震相分析,得到了该地震序列较为可靠的震源深度分布,并与CAP波形反演、双差定位、sPn震相、Hyposat等方法定位的结果进行了对比。结果表明,sPL震相测定的近震震源深度较为可信,该地震序列的震源深度分布在9~11km范围内。