根据截断的G-R模型计算东北地震区震级上限

震级上限是指一个地区可能发生地震的最大震级,其概率意义为发生超过该震级地震的概率几乎为0.在有些地区,由于对其内部的地震构造研究和认识存有局限性,很难根据构造或者地质学的原则来确定震级上限.因此,根据数学模型,采用统计手段,使用地震活动性资料来计算震级上限的估计值是一种可行的方法.本文根据截断的G-R关系模型,采用最大似然计算方法,使用东北地震区的地震目录,计算了东北地震区震级上限,结果表明东北地震区的震级上限应为Mu=7.5左右.计算中我们考虑了不同震级的转换、震级误差的修正以及计算方法的影响.最终结果表明,不论采用何种方案进行计算,东北地震区的震级上限值均始终保持在7.5左右,这说明我们采用本文中方法计算得到的东北地震区的震级上限值是合理可信的,同时也说明在以往的研究中对东北地震区震级上限的估计大都是偏小的.

东北地震区b值和地震年平均发生率的统计分析

震级和频度关系式中的b值和地震年平均发生率是表征一个地区地震活动性的重要参数,也是地震危险性概率分析中不可缺少的计算参数。本文根据当前的地震目录,利用数理统计的方法给出了东北地震区的b值和地震的年平均发生率。该研究成果对在本区开展地震安全性评价和地震预报具有重要的参考价值。

东北地震区小震资料完整性分析及其对地震活动性参数的影响研究

以东北地震区为例,基于G-R关系的震级-频度分布原理,研究了东北地震区最小完整性震级MC的时间分布特征和各时段的空间分布特征,统计了研究区内的地震活动性参数,探讨了小震资料完整性分析对地震活动性参数和地震危险性计算结果的影响。研究表明,对区域小震资料进行完整性分析,可以在低水平地震活动地区获得较准确的地震活动性参数,更好地反映了该区未来的地震活动趋势。本文的研究方法和结论可供地震资料完整性分析和地震活动性分析时参考。

东北地震区地震趋势的小波分析

根据中国地震局推广软件中所给出的地震区划分,运用小波分析方法,对东北地震区的地震时序特征进行了分析和研究,得出:东北地震区的地震活动存在着10年、20年和30年的显著主周期。按照这个周期规律,结合测震学的分析方法,分析了未来东北地震区的地震活动趋势,认为东北地震区第五活跃期到2009年结束。从地震能量释放和地震频度上看,未来发生5级以上地震的可能性不大。

Relocation of Earthquakes in the Northeastern Tianshan Mountains Area and Improvement of Local 1-D Crustal Velocity Model

We apply three methods to relocate 599 earthquake events that occurred from August 2004 to August 2005 in the northeastern Tianshan Mountains area ( 85°30' ～ 88°30'E,43°00' ～ 44°40' N ) by using travel times recorded by regional seismic network and 10 portable seismic stations deployed around the Urumqi city. By comparing the reliability of different results,we determined a suitable location method,and an improved 1-D crustal velocity model of the study area. The uncertainty of earthquake location is significantly reduced with combined data of seismic network and portable stations. The relocated events are clearly associated with regional tectonics of the northeastern Tianshan Mountains area, and are also in agreement with the existence of active faults imaged by deep seismic reflection profile. The relocated seismicity discovers some potential traces of buried active faults,which need to be validated further.

Seismic volcanostratigraphy of large, extrusive complexes in continental rift basins of Northeast China：Analysis of general bedding patterns in volcanostratigraphy and their seismic reflection configurations

The aim of this work is to establish volcanic seismic reflection configuration models in the rift basins of Northeast China from a new perspective,the volcanostratigraphic structure.Accordingly,the volcanostratigraphic structure of an outcrop near the Hailaier Rift Basin was analyzed to understand the characteristics and causal factors of physical boundaries.Further,3D seismic reflection data and analysis of deep boreholes in the Songliao Rift Basin were used to establish the relationship between volcanic seismic reflection configurations and volcanostratigraphic structures.These studies suggested that in volcanic successions,physical boundaries coincide with volcanic boundaries,and their distributions are controlled by the stacking patterns of volcanic units.Therefore,volcanic seismic reflection configurations can be interpreted in terms of the stacking patterns of volcanic units.These are also referred to as general bedding patterns in volcanostratigraphy.Furthermore,four typical seismic reflection configurations were identified,namely,the chaotic,the parallel continuous,the hummocky,the multi-mound superimposed and the composite.The corresponding interpretation models comprised single massive unit,vertical,intersectional,lateral multi-mound,and composite stacking patterns.The hummocky and composite reflection configurations with intersectional and composite stacking patterns are the most favorable for the exploration of volcanic reservoirs in rift basins.

Analysis of Small Earthquake Activities before Medium-strong Earthquakes in Northeast China

13 earthquakes with M 〉 5.0 have been recorded in the northeast region of China since 1970, among which eight medium-strong earthquakes are independent in space and time. Studies of seismicity before these eight medium-strong earthquakes show that small earthquake activity was enhanced before the occurrences. Though seismicity increase is a common phenomenon in the northeast China region, we have difficulty in predicting the medium-strong earthquakes by this phenomenon alone. In order to predict medium-strong earthquakes through se｜smicity increase, this paper tries to propose a new method that calculates small earthquake frequency through the changing pattern of small earthquake activities based on the characteristics of small earthquake activity in the northeast China region. The results show that we can get the obvious anomaly frequency of small earthquakes before medium-strong earthquakes through the new method, and can obtain a medium to short term anomaly index for the northeast China region.

Preliminary Study on Seismic Anisotropy in the Crust in the Northeast of Hainan

With SAM shear-wave splitting analysis,shear-wave splitting parameters at two stations of the digital seismic network in the northeast of Hainan are obtained based on the data from the Hainan Digital Seismic Network from 2000 to 2013. The results show that the predominant polarization direction of fast share-wave represents the direction of in-situ maximum principal compressive stress. The predominant polarizations of Qixingling( QXL) seismic station are in the NEE direction,which is different from the direction of principal compressive stress of the Hainan area,but same as the strikes of faults in the NE direction,which means that the local tectonics and stress fields are complicated. The predominant polarization of Qingshanling( QSL) seismic station is in the NNE-NS direction,which indicates the tectonic significance of the strikes of NNE-trending faults.At the same time,the study confirms that the predominant polarizations of the stations located on active faults or at the junctions of several active faults are parallel to the strikes of faults which control the earthquakes used in this analysis, and the predominant polarizations are scattered,which indicates the complicated background of fault structures and stress distribution.

Characteristics of PmP phases from earthquakes and their role in crustal tomography:An active volcanic area example,northeastern Japan

Later earthquake-sourced PmP phases have the potential to significantly improve ray coverage and resolution of crustal tomography methods,as their trajectories are quite different from those of shallower P phases.This paper analyzes the characteristics of later PmP arrival times from earthquakes with different focal depths.The results show that PmP arrival time differences from earthquakes at a range of focal depths are gradually lowered with increasing offset.We found that where the first recorded P-wave phase was the intra-crustal refraction phase(Pg),the differences in arrival time between Pg and PmP phases decreased with increasing focal depth at an offset of less than 120 km.Where the first P-wave phase is the upper mantle refraction phase(Pn),the difference in arrival times between Pn and PmP phases became larger with an increase in focal depth at an offset of more than 150 km.A total of 394 PmP phases and 3356 first P phases were picked from seismograms in the active volcanic area of northeastern Japan,according to the characteristics of calculated arrival times,amplitudes and particle motions.These were used to investigate the role of PmP phases in crustal tomography beneath an active volcanic region.Results of the detailed resolution analysis show that the addition of PmP data can improve significantly the resolution of the lower crustal structure in tomographic images.After the PmP data were included in the tomographic inversion,the path of upwelling magma,along which a series of low-frequency microearthquakes is clearly distributed,was better imaged.These results suggest that the PmP phase has an important role in detailed crustal tomography.