Three—dimensional P velocity structure in Beijing area

A detail three-dimensional P wave velocity structure of Beijing,Tianjin and Tangshan area(BTT area)was deter-mined by inverting local earthquake data.In total 16 048 Pwave first arrival times from 16048 shallow and mid-depth crustal earthquakes,which occurred in and around the BTT area from 1992to 1999were used.The first arrival times are recorded by Northern China Unived Telemetry Seismic Network and Yanqing-Huailai Digital Seismic Network.Hypocentral parameters of 1 132 earthquakes with magnitude ML=1.7-6.2 and the three-dimensional P wave velocity structure were obtained simultaneously.The inversion result reveals the com-plicated lateral heterogeneity of P wave velocity structure around BTT area.The tomographic images obtained are also found to explain other seismological observations well.     

台湾及邻近地区地震活动间歇性的一些特征

从地震活动间隔时间的角度出发,结合1970～2003年台湾及邻近地区的地震活动,对其震级一最大间隔时间对数的关系进行了分析。从地震活动等待时间的角度出发,分析了地震活动次数百分比与等待时间的关系,最后简略地介绍了地震活动次数百分比等值线图的一些特征。     

云南及邻区中强震连发和平静与强震关系研究

系统研究了1925年以来云南及邻区5级以上地震的时间分布特征, 分别给出了云南及邻区5级以上地震连发和平静的定义。 分析了中强震连发、 平静的一些基本特征, 研究了5级以上地震连发、 平静事件与该区强震活跃、 平静过程的关系。 这些分析结果对云南及邻区的地震趋势预测有一定实际意义。     

Seismic tomography of Yunnan region using short-period surface wave phase velocity

Introduction The Yunnan region is located on the east margin of the collision zone between the Indian and Eurasian plates; it belongs to the south section of the N-S Seismic Belt of China and is the junc-ture of the Yangtze metaplatform, Songpan-Garz?fold system, Sanjiang fold system and South China fold system. This region has complex tectonic movements, crisscross faults and frequently occurring strong earthquakes, and hence it is one of the regions with the strongest earthquake ac-tivi…     

青藏高原东部及邻区地震断层面上的潮汐应力触发效应

根据已发布震源机制解目录（哈佛大学CMT）,将青藏高原东部及邻区划分为5个构造应力场分区,并对各分区的地震逐个计算其发震断层面上的固体潮汐正应力、剪应力、库仑破裂应力及相位角,分析潮汐应力分量对不同类型发震断层的作用效果及其随深度变化特征.基于库仑破裂应力判断准则,研究潮汐应力对各种类型地震的触发作用;基于Schuster检验方法,统计分析潮汐应力对各个震级档、不同构造类型地震的影响.综合运用上述两种分析方法,探讨潮汐应力对不同震级地震以及处于不同构造块体、发震断层、震源深度地震的触发机制.结果表明,潮汐应力对印度块体和拉萨块体的正断和逆断型地震,滇缅泰块体、印支块体和松潘-甘孜块体的走滑和斜滑型地震,川滇菱形块体的斜滑型地震均存在不同程度的触发效应,且触发效应的强弱依赖于震源深度、震级大小、发震断层类型及其所处区域构造应力场.     

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...     

Surface wave tomography of the crust and upper mantle of Chinese mainland and its neighboring region

Introduction The three-dimensional S wave velocity of Chinese mainland and its neighboring region in-verted by surface wave dispersion data plays an important role in studying the lateral variation of lithosphere and geodynamic process, and understanding the forming and evolution of Chinese mainland and the relationship between shallow and deep structures. The three-dimensional veloc-ity structures of China and its major tectonic blocks were respectively studied by SONG, et al (1993), ZHOU…     

广东及邻区地震活动特征及近期地震危险性分析

通过对1067～2002年广东及邻区地震活动的研究结果表明，本区6级以上地震主要发生在沿海近海区域，7级以上地震全部位于海中，陆地的中强地震主要发生在北东向和北西向断裂带或其交汇部位，本区陆地不具备孕育7级地震的地质条件。中强地震存在明显的活动周期，当前已进入平静时段。计算了本区各地的地应力，并分析GPS有关观测结果，再结合地震活动参数和有关数理统计结果，认为2005年前本区发生6级以上地震的可能性不大，但存在发生ML5级地震可能。     

利用速度结构与震源参数联合反演算法研究天津及邻近地区小震重定位特征

利用2002年1月至2008年12月天津地震台网产出的初至P波走时资料,通过震源与速度结构联合反演算法,计算出天津及邻近地区三维P波速度结构的优化模型,同时获得1 738次中小地震的重新定位结果.结果表明,天津及邻近地区中小地震分布具有与强震相同的地壳深部介质背景,主要分布在高低速度过渡带;天津及邻近地区中小地震震源深度重新定位后更集中分布在10-15 km深度范围内.     

Three-dimensional crustal P-wave velocity structure in the Yangbi and Eryuan earthquake regions,Yunnan, China

A magnitude 5.5 earthquakes occurred in Eryuan County, Dali Bai Autonomous Prefecture, Yunnan Province, China, on March 3. And a magnitude 5.0 earthquake occurred in the same place on April 17, 2013, i.e., 45 days later. Then, on May 21, 2021, multiple earthquakes, one with magnitude 6.4 and several at 5.0 or above, occurred in Yangbi County, Dali Bai Autonomous Prefecture, Yunnan Province, China. All of these occurred in the Weixi-Qiaohou-Weishan fault zone. In this study, 1,874 seismic events in Yangbi and Eryuan counties were identified by automatic micro-seismic identification technology and the first arrivals were picked up manually. Following this, a total of 11,968 direct P-wave absolute arrivals and 73,987 high-quality P-wave relative arrivals were collected for joint inversion via the double difference tomography method. This was done to obtain the regional three-dimensional fine crustal P-wave velocity structure. The results show that the travel time residuals before and after inversion decreased from the initial –0.1–0.1 s to –0.06–0.06 s. The upper crust in the study area, which exhibited a low-velocity anomaly, corresponded to the basin region; this indicated that the low-velocity anomaly in the shallow part of the study area was affected by the basin. Results also showed some correlation between the distribution of the earthquakes and velocity structure, as there was a low-velocity body Lv1 with a wide distribution at depths ranging from 15–20 km in the Yangbi and Eryuan earthquake regions. In addition, earthquakes occurred predominantly in the high-low velocity abnormal transition zone. The low-velocity body in the middle and lower crust may be prone to concentrating upper crustal stress, thus leading to the occurrence of earthquakes.     

青藏高原东北缘地壳三维速度结构

本文用1980—2000年M≥1.5的2 032个天然地震事件的38 052个〖AKP-〗、〖AKS-〗、Pm、Sm、Pn和Sn震相到时及人工地震测深给出的Moho面形态资料,利用地震层析技术反演了32°~40°N, 100°~108°E区域内地壳地震波速度结构.从层析成像图象中可以得到,本区的地壳可分成4个层位.第1层（埋深约在0~3 km）为沉积层, 速度梯度约为0.2 s-1;第2层（埋深约在3~17 km）为上地壳, 其顶部速度梯度约为0.1 s-1, 下部速度横向变化较大且存在低速块体;第3层（埋深约在17~36 km）为中地壳, 速度梯度约为0.03 s-1;第4层（埋深约在36 km—Moho）为下地壳, 是一个契形层,总的趋势是西厚东薄,青藏高原较厚逐渐向鄂尔多斯地块和扬子准地台方向变薄,各处的地震波速度梯度不尽相同.     

Three-dimensional seismic velocity tomography of the upper crust in Tengchong volcanic area, Yunnan Province

Introduction Tengchong is one of youngest volcanic areas in Chinese mainland. Since Pliocene, the volcanoes have erupted several times. Nowadays, the thermal activity is very intensive there. The possibility of re-eruption and the reserve of geothermal energy in the area are the questions to which the publics pay much attention, and the volcanists and seismologists dedicated. HAN, et al (1996) reviewed all of the studies carried out in Tengchong area. In the late 1990s, an integrative volca…     

Mantle structure from inter-station Rayleigh wave dispersion and its tectonic implication in western China and neighboring regions

We processed more than 3000 inter-station great circle paths to determine the phase velocity for the fundamental mode of Rayleigh wave, and finally arrived at 110 paths of high quality dispersion data, which show good spatial coverage in western China and neighboring regions. Rayleigh wave phase velocity dispersion model WChina1D was obtained and compared with previous global and regional models. Phase velocity maps from 15 to 120 s were inverted and the maps of 20, 40, 80, and 120 s are presented in this paper. Checkerboard tests show the average lateral resolution in our area of interest is about 7°. Our tomographic results corroborate a prominent low-velocity anomaly lying mainly in the lower crust and uppermost mantle in the Chang Thang terrane. The apparent low-velocity anomaly also appears in the wide area of northeastern Tibet in the crust and upper mantle. The low-velocity area around southeastern Tibet may be created by the southeastern migration of the low-velocity mass of the Tibetan plateau. The eastern Tarim shows structure with higher velocities relative to that of central Tarim. A large-scale low-velocity anomaly is clearly seen in central and western Mongolia. Our high quality measurements were also used to evaluate the CUB global shear velocity model [Shapiro, N., Ritzwoller, M., 2002. Monte-Carlo inversion for a global shear-velocity model of the crust and upper mantle. Geophys. J. Int. 151, 88-105] of the crust and upper mantle. The 40 s Rayleigh phase velocity map predicted from CUB model shows an apparent discrepancy with our measurements in western China and western Mongolia, which implies a higher estimated (about +1-2%) phase velocity model in these regions, probably due to the Gaussian smoothing condition in their tomography inversion.     

Three-dimensional velocity structure and seismicity of Mt. Etna Volcano, Italy

A new set of three-dimensional velocity models beneath Mt. Etna volcano is derived in the present work. We have used P- and S-wave arrivals from local earthquakes recorded at permanent and temporary seismic networks installed since 1980. A set of 1249 earthquakes recorded at more than four seismic stations was selected for traveltime inversion. The velocity models obtained by using different data selection criteria and parametrization display similar basic features, showing a high P-wave velocity at shallow depth in the SE quadrant, in close connection with a high gravimetric Bouguer anomaly. This area shares a low V_p/V_s ratio. High P-wave velocities and high V_p/V_s ratios are obtained along the central conduits, suggesting the presence of dense, intrusive magmatic bodies extending to a depth of about 20 km. The central intrusive core is surrounded by lower P-wave velocities. The relocated earthquake hypocenters also display the presence of an outward dipping brittle region, away from the central conduits, surrounding a ductile zone spatially related to the high P-wave velocity anomalies located in proximity to the central craters.     

云南地区地壳速度结构的层析成像研究

利用地震波到时和体波层析成像方法反演了云南地区的P波速度结构,根据不同深度的速度异常分析了主要断裂和区域动力作用的深部效应,揭示出壳内低速层的分布范围以及与下地壳流动的联系.研究结果表明,哀牢山—红河断裂两侧的地壳速度结构存在明显的差异,滇中地区的速度异常分布与小江断裂、元谋断裂、程海断裂等南北走向的断裂一致,反映了青藏东部地壳块体顺时针旋转产生的构造效应;滇西南的速度异常分布与哀牢山—红河断裂、无量山断裂、澜沧江等断裂的走向平行,显示了印支块体朝东南方向挤出产生的影响;沿着南汀河断裂分布的低速异常则与印缅块体侧向挤压引起的构造活动有关.壳内低速异常具有分层和分区特征:在哀牢山—红河断裂西侧和澜沧江之间主要分布在地壳中上部,在小江断裂和元谋断裂附近分布在地壳中下部,在滇中地区则广泛分布于地壳底部至莫霍面附近,东、西两侧分别受到小江断裂和哀牢山—红河断裂的限制.其中攀西地区的低速异常与小江断裂和元谋断裂在此附近交汇形成的热流传输通道以及张裂时期强烈的壳幔热交换有关;在哀牢山—红河和澜沧江地区,除了印支块体向东南方向的挤出之外,印缅块体的侧向挤压和向东俯冲也对地壳深部的构造变形产生了一定的影响,由此引发的地幔上涌将导致热流物质沿着断裂通道进入地壳形成低速层.因此,哀牢山—红河断裂不仅在地壳浅部是分隔印支块体和华南块体的地质界限,也是控制两侧区域深部构造变形和壳内韧性流动的分界.     

S-wave velocity and Poisson''''s ratio structure of crust in Yunnan and its implication

Receiver function of body wave under the 23 stations in Yunnan was extracted from 3-component broadband digital recording of teleseismic event. Thus, the S-wave velocity structure and distribution characteristics of Poisson's ratio in crust of Yunnan are obtained by inversion. The results show that the crustal thickness is gradually thinned from north to south. The crustal thickness in Zhongdian of northwest reaches as many as 62.0 km and the one in Jinghong of further south end is only 30.2 km. What should be especially noted is that there exists a Moho upheaval running in NS in the Chuxiong region and a Moho concave is generally parallel to it in Dongchuan. In addition, there exists an obvious transversal inhomogeneity for the S-wave velocity structure in upper mantle and crust in the Yunnan region. The low velocity layer exists not only in 10.0-15.0 km in upper crust in some regions, but also in 30.0-40.0 km in lower crust. Generally, the Poisson's ratio is on the high side, however it has a better co     

河北省南部及邻区地壳P波速度结构三维反演

1980—2012年河北省及邻区测震台网地震记录,使用了河北省南部及邻区（34.0°—38.0°N,112.0°—118.0°E）63个固定地震台站和4 540个地震事件,得到27 709条P波到时数据,采用速度结构与地震位置联合反演的方法,获得研究区内地壳P波三维速度结构,重新确定中小地震震源位置。速度结构揭示：研究区域内地壳的P波速度结构存在明显的横向不均匀性,在10—25 km深度上横向不均匀性更加显著;大地震基本发生在速度异常体或高低速交界区域。地震重新定位结果显示：地震P波走时均方根残差（RMS）从1.68 s降到0.82 s;地震呈明显条带状分布,震源深度与地质构造年代具有一定负相关性。     

辽宁及邻区背景噪声相速度结构研究

收集辽宁及其周边地区（吉林、河北、山东、内蒙）70个宽频带地震仪2012年连续背景噪声波形数据,基于地震背景噪声层析成像方法,得到研究区面波群速度及相速度图像。利用台站对互相关方法,提取瑞利面波格林函数,采用时频分析法（FTAN）获取2 416条相速度频散曲线,从中筛选1 661条信噪比较高的频散曲线。将研究区以0.25°×0.25°进行网格化,采用Ditmar等提出的层析成像反演方法,得到周期10—40 s的瑞利面波群速度及相速度结构分布图。与群速度结果相比,分辨率更高,研究区大部可达0.5°×0.5°（局部可达0.25°×0.25°）。结果表明,辽宁地区地壳及上地幔面波相速度结构存在显著的横向不均匀性。在周期10—15 s的群速度图中,浅层及中上地壳速度分布与研究区地形地貌及主要地质构造单元具有较好的对应关系,盆地及沉积层低速,山区隆起高速,且在高低速转换带多为地震孕震区;在周期20—30 s相速度结构图中,下地壳至上地幔顶部深度范围内,相速度速度结构主要受地壳厚度及渤海湾内巨厚沉积层的影响,在海城至大连区域内出现的低速异常推测为地下热物质上涌;随着深度的增加,在周期30—40 s的相速度图中,速度分布逐渐受控于莫霍面起伏,明显变化出现在辽东半岛,由高速变为低速。     

蒙古及邻区上地幔顶部Pn速度结构

利用78364条Pn射线的走时资料,采用地震层析成像方法反演蒙古及邻区上地幔顶部Pn速度结构.反演结果表明,蒙古及邻区Pn平均速度为8.08 km/s,横向速度变化量从-0.39 km/s至+0.30 km/s.速度高异常区主要分布在阿尔泰山地区及准噶尔盆地、塔里木盆地等地,在阿尔泰山地区Pn速度最大异常达+0.30 km/s.速度偏低的地区主要在贝加尔湖、华北平原、渤海湾等地,在贝加尔湖西南呈现出强烈的低速度异常达-0.39 km/s,可能与该区新生代的火山活动有关.     

河南及邻区中等地震前地震释放应变能速率B值时空演化

对河南及邻区中等地震前地震释放应变能速率B值进行时空扫描，通过对1970年至今所有ML≥4．7级地震前B值的时空演化的对比分析得出以下结论：中等地震前B值出现高值异常，且在发震前一年内结束高值，且绝大多数地震发生在B值高异常区内。