硕士学位论文摘要.doc

硕士学位论文摘要Abstract of Thesis For Masters Degree专业：固体地球物理学Major：Solid geophysics研究方向：地震波理论与应用Research：Theory and Applications of Seismic Waves论文题目：地震波到时与视出射角联合定位方法研究Topic：Study of Seismic Location Method using Seismic Arrival-time and Apparent Emergence Angle研究生：李稳Postgraduate：Li Wen指导教师：张元生Tutor：Zhang Yuansheng答辩日期：2009.07.01Date of Reply：2009.07.01学位授予单位：中国地震局兰州地震研究所Awarding Place：Lanzhou Institute of Seismology摘 要地震定位是指确定地震的震源位置和发震时刻。准确的地震定位结果对地震活动性分析、震源机制求解以及地球内部结构探测等问题非常重要。地震定位精度除受台网布局、可用定位震相、到时读数精度、地壳速度模型等因素影响外，还与定位方法密切相关。研究地震定位方法是地震学中一个基本和常新的课题。经过近一个世纪的努力，地震学家发展了多种定位方法，如交切法、Geiger法、SSH法、双差法等。这些定位方法侧重点不同，应用环境不同，各有其优、缺点。目前我国已在全国范围内建立了数字地震观测台网，数字地震观测技术得到了广泛应用。结合这些有利条件，在深入学习传统定位方法的基础上，本论文提出了联合利用地震波到时和视出射角参数进行地震定位的方法地震波到时与视出射角联合定位方法。提高地震定位结果中震源深度的精度是本论文的创新点。通过充分挖掘地震波所携带的丰富信息，增加独立的观测参数以减轻地震定位反问题的多解性是本论文的理论依据。本论文针对EVT格式的波形数据，编写了专用的可视化波形处理分析软件，可确保求取视出射角参数的准确与高效。建立了联合定位方法的目标函数(公式1)。使用蒙特卡洛法作为反演方法实现其最优化计算过程。进行了理论计算和实际地震资料处理。对定位结果进行了误差分析与评价。 （1）上式可写成： （2）式中，i是台站序号，N是台站总数，为第i个台站的观测走时，为理论走时；j是具有视出射角的台站序号，M是具有视出射角参数的台站总数，为第j个台站的观测视出射角值，为第j个台站的视出射角理论值。通过理论计算，可知在模型准确的情况下，对于本论文所采用的模拟数据，仅利用到时数据的蒙特卡洛法和双差法定位结果已具有精确的震中位置，定位结果水平向误差约为0.2公里。但深度误差相对较大，这在深度对比中表现得更加明显。仅利用到时数据的蒙特卡洛法和双差法定位结果深度平均误差分别为0.54公里和2公里。相对而言，利用到时与视出射角联合定位法进行定位的定位结果，在不失震中准确度的基础上具有了更高的深度准确度。利用蒙特卡洛法实现联合定位的定位结果和利用双差法实现联合定位的定位结果其深度平均误差分别为0.21公里和0.35公里。分析造成这种差异的原因，是由于视出射角参数对深度的敏感程度高于到时数据。本论文针对2004年6月的临泽震群、2002年12月的玉门震群进行了新方法的实际地震资料处理应用。这两个震群均发生在数字地震观测台网建成以后，被甘肃省测震台网有效监测。发震地区周围有嘉峪关、高台、肃南等多个固定台站。这些台站监测获得了震群地震事件清晰的数字化波形记录并提供了准确的多种震相到时读数。前人在临泽、玉门地区的层析成像、地震定位和地质构造研究成果可以为建立准确的速度模型提供参考和依据。另外，这两个震群的时间、空间分布集中，益于进行多种定位方法的对比研究。已发表的地震定位、地质构造研究成果，可以为新方法定位结果提供对比、参照。研究这两个震群，对于验证地震波到时与视出射角联合定位方法的实际应用效果十分有利。这些地震事件的台网初步定位结果和台站、到时数据由地震观测报告获得。视出射角参数由甘肃测震台网提供的波形资料处理求得。本论文利用蒙特卡洛法、双差法等传统的到时定位方法和地震波到时与视出射角联合定位方法对这两个震群的地震事件进行了重新定位。将台网初步定位结果、重新定位后的定位结果成像并进行对比分析，最后进行定位结果的残差分析。分析结果表明利用地震波到时与视出射角联合定位方法的定位结果比利用其它方法的定位结果更加合理、可信。联合定位结果能更有效地反映发震断层的深部信息，更有利于对断层要素的研究勾画。联合定位结果可为地质构造研究提供准确的参考与依据。本论文通过理论计算和实际地震资料处理分析，证明了利用地震波到时与视出射角联合定位方法确实可以提高地震定位对震源深度的分辨，从而提高地震定位精度。前人的研究结果指出，利用一次中强地震及其余震序列的空间分布(三维)来研究发震构造和发震机制有用而且必要，但前提是地震序列中各次地震的三维定位必须达到足够的精度。地震波到时与视出射角联合定位方法提供的定位结果满足精度上的要求。数字地震观测技术的应用将对地震学的发展起重要的推动作用。地震定位精度受诸多因素的影响，在现有条件下，通过增加对地震波视出射角(尤其是震中附近台站监测到的地震波视出射角)的利用，提高地震定位精度，获取更准确的地震深度信息，对断层、构造研究有实用价值。联合定位方法在现代数字化地震监测定位中具有广泛适用性。研究利用到时与视出射角联合定位是一次有益的尝试，但在研究过程中也发现了一些亟待解决的问题。比如，利用蒙特卡洛法进行反演时，计算工作量大，收敛速度慢。目前模拟退火法、遗传算法等启发式反演方法能极大地提高计算效率，将这些反演方法应用于联合定位是下一步的研究目标。关键词：地震波到时，视出射角，联合定位AbstractThe determination of earthquake locations and origin time is intituled earthquake locating. Its result is important to seismic activity analysis, focal mechanism solution and earth interior exploration.The earthquake locating accuracy is influenced by seismic network distributing, arrival-time accuracy, velocity model accuracy, usable seismic phases and locating method. Study locating method is an elementary and important problem in seismology.Through great efforts, a lot of locating methods were developed by seismologists. Such as cross bearings method, Geiger method, SSH method, double-difference location algorithm, etc. These methods have different emphases, applied environments and relative merits. So far, the nationwide digital seismograph network has been established and the digital seismical technique has been widely used. To use these advantages, base on studying lots of locating methods, this paper present a new location method which use both seismic arrival-time data and apparent emergence angles to locate earthquakes. Its strongpoint is acquiring the focal depth accuracy. Its theoretical foundation is lightening the multiplicity of inverse problem through abstracting the effective information taken by earthquake waves and adding absolute observable information.To insure the accuracy and efficiency of extracting apparent emergence angles, appropriative software for disposing the EVT wave data was wrote. In this paper, the objective function was founded and Monte Carlo method was used to realize its optimization. The theoretical calculation and actual seismic data disposition were actualized. In the end, error analysis had been done. (1)viz., (2)In the expressions, i is the serial number of digital seismic station, N is the total number of stations, is observed arrival-time value of No. i station, is theoretical arrival-time value of No. i station, j is the serial number of station which offered apparent emergence angle, M is the total number of stations which offered apparent emergence angles, is observed apparent emergence angle value of No. j station, is theoretical apparent emergence angle value of No. j station.The theoretical calculation results validated that, if exact velocity model was used, we could work out exact earthquake locations by using the arrival-time data only. The horizontal error was 0.2 kilometers. But the depth error was comparatively big. The depth error of locating result using Monte Carlo method is 0.54 kilometers. The depth error of locating result using double-difference algorithm is 2 kilometers. Relatively, the multiparameter locating results using both of seismic arrival-time and apparent emergence angle are more exact on earthquake depth. The depth error of multiparameter locating results using Monte Carlo method is 0.21 kilometers. The depth error of multiparameter locating results using double-difference algorithm is 0.35 kilometers. The causation maybe is that, the arrival-times sensitivity to hypocentral depth is lower than the apparent emergence angles sensitivity to hypocentral depth.In this paper, the new multiparameter seismic location method had been used on the study of Linze earthquake swarm and Yumen earthquake swarm. These earthquake swarms were monitored by Gansu Digital Seismic Network. Multiple stations such as Jayuguan Station, Gaotai Station, Sunan Station, etc. got clearly digital seismic wave data and offered exact arrival-time data of multiple seismic phases. The seismologists productions on the area or earthquake swarms are propitious to founding velocity model and analyzing the seismic location results which worked out by using the new multiparameter method. These earthquakes initial earthquake locations and , arrival-time data were offered by Gansu Seismic Report. The apparent emergence angles were calculated by using the digital seismic wave data. This paper used manifold seismic location methods to locate these earthquakes. The results indicated that the multiparameter seismic location results are more believable. Using the multiparameter locating results, we could more clearly reflect the faults deep-seated information and the faults essentials. The multiparameter locating results could offer reference frame to the geological research.In conclusion, the seismic location results validated that using the multiparameter seismic location method could really improve the resolving power to the focal depth. And then the seismic location accuracy is improved. This method is valuable for studing fault parameters and fault spreading. The diagrams of earthquake locations calculated by using the multiparameter seismic location method is more propitious to studying the fault deep-seated information and fault parameters.The seismologists research results pointed out that, using the earthquake locations to study the seismogenic fault and earthquake mechanism is feasible and required. The premise is that the earthquake locations are enough exact. The multiparameter seismic locating results could reach the require of precision.The seismic location is influenced by several elements. On existence conditions, raise the seismic location accuracy by increasing the use of apparent emergence angles, especially the nearby stations apparent emergence angles, is practicability. The multiparameter seismic location method which use both seismic arrival-time data and apparent emergence angles is fit for present-day digital seismic network.The study of seismic location method using seismic arrival-time and apparent emergence angle is an profitable attempt. But in the research process, were found some topics also. Such as, the workload is too big and the velocity of convergence is too slow when using the Monte Carlo method to realize optimization. So far, the Simulated Annealing method and the Genetic Algorithm method could obviously improve the