Based on microearthquakes fine relocations and focal mechanisms, the paper analyses the causes of clustered microseismicity in Puyang, Henan. The relocated results given by hypoDD shows that the hypocenters of most microearthquakes are situated at the trunk fault of Liaocheng-Lankao fault zone, and its distributions accord with the fault's attitude. Focal mechanisms of 5 events with ML≥3.5 show that observed waveforms can be well explained by the double couple model. There are mainly strike-slip mechanisms in smaller events, with quadrantal polarities. On the basis of relative materials on geology and tectonic backgrounds of oilfield, the paper discusses inductive relationship between fluid injection for oil-production and microseismicity in this area.

1668年在山东郯城附近发生的81/2级巨大地震,是有史料记载以来发生在中国东部的最大地震.该地震发生在郯庐断裂带山东区段,震源区现代小震依然频繁.本文以震源区附近重新定位的百余个现今中小地震基本参数,反演得到1668年郯城81/2级大震震源断层产状:震源断层走向21.6°,倾角为89.5°,滑动角为148.9°,震源断层长度约180km,下界深度约为32 km,上界埋深约为4km左右,为北北东走向直立的右旋近走滑断层.震源断层在地壳浅表对应沂沭断裂带东地堑的安丘—莒县断裂(F5).根据81/2级大震地表地震断层和烈度分布研究成果对反演结果进行了分析,并结合震源区地震深度分布、地震波速度剖面等对81/2级地震的基本参数进行了讨论,认为各种结果之间能够相互验证,反演获得了理想结果.研究证明,对于震源区现代中小地震资料丰富的历史大地震,用该方法反演震源断层三维产状和错动性质是可行的.

Using the double difference earthquake location algorithm,we relocate more than 400 moderate and small earthquakes near the epicenter of 1668 Tancheng 8(1/2) earthquake since 1974.The relocated result shows that the modern moderate and small earthquakes were still concentrated in the Tancheng earthquake rupture zone.The strike of the bandy concentrated zone accords with that of the generating Anqiu-Juxian fault speculated by geological surveying.

用双差定位方法对1668年郯城81/2级地震震中附近1974年以来400余个中、小地震重新进行定位.结果显示现代中、小地震震中分布仍集中于地震破裂带上,带状集中区与地质考察推测得到的发震断层安丘-莒县断裂的走向吻合.

On the assumption that current state of earthquake activities in North China will go on,based on Benioff strain released series of different tectonic belts since 1970,many types of non-linear functions have been adopted to fit the strain cumulative release trend.By the proximal and optimal fitting model,the author gives the forecasts of Benioff strain release in the coming 1 to 3 years.According to the linear magnitude frequency law,the author also gives estimation of corresponding max magnitude for each tectonic belt.

According to the digital seismic data of 217 ML≥1.0 earthquakes from Oct.2008 to Sep.2009 in Shandong and its adjacent areas recorded by Shandong seismic network,the VP/VS ratio is calculated,and the earthquake tendency in the region is analyzed by the variations of VP/VS.The result shows that the seismicity and the variations of VP/VS did not present obviously anomalous characteristics in the region.

<正>将一定范围内的地震活动视为随机时间序列,则可以用线性回归的方法对未来的地震活动情况进行预测(Vere-Jones,1995)。在地震活动的研究中常采用自回归模型。

In order to study the crustal movement of Shandong and surrounding areas before and after Wenchuan M s8.0 earthquake,we analyzed the baselines between Taian(TAIN) and several fiducial stations in different blocks by using SDFT Period Estimate method.The preliminary results showed that there were obvious exceptional annual variations of baseline TAIN-XIAN and TAIN-WUHN before Wenchuan earthquake.The eastward movement velocity of GPS fiducial stations in Shandong and surrounding area was decreasing after the earthquake,we conclude that the eastward driving force on the North China block weakened,It shows that the Wenchuan earthquake alleviated the Shandong and surrounding areas' recent earthquake situation.

The geological tectonic structure of northeast margin of the Tibetan Plateau correlates with that of Qinling-Dabashan region.The out flow of material in Tibetan Plateau lithosphere and regional structures interaction is the major tectonic stress acting on plate of the south part of North China.Based on these understandings,the seismic activity in south part of north China before 4 large earthquakes(M≥8) occurred on northeast margin of the Tibetan Plateau is analyzed.Seismic activity abnormity close to large earthquake epicenters is not obvious,but seismic activity in south part of north china is distinct.The process of seismic activity abnormity in south part of north china is visibly correlative with the strong earthquake brewing and occurring in northeast part area of Tibetan Plateau edge,The seismic situation display in outside areas give us some new idea on estimation the strong earthquake situation in northeast part area of Tibetan Plateau edge.

The earthquake-monitoring capacity of Shandong digital seismic network is calculated by using the broad-band digital data of background noise record of 44 stations when there is no earthquake record or other disturbance,and also inspected by using the blast and seismic records of the tenth five-year plan network during test operation.The calculation results are in accordance with actual observation.In addition,the results show that the earthquake monitoring capacity has realized ML≥1.6 in Luxi area,Huanghai Sea and BohaiSea,ML≥1.3 in central and east area,ML≥0.7 in some region of Jiaodong Peninsula and some parts of the South.

The formula of seismic intensity attenuation for Shangdong and its adjacent areas is fitted by using 70 isoseismal lines from 34 earthquakes in this region.Meanwhile based on the difference of landform and geological structure characteristic,the region is divided into soil covered area and bedrock exposed area,the individual formula of seismic intensity attenuation for both areas are fitted also.

The moderate and small earthquakes in Chang Dao area(35.8°～38.7 N°, 119.4°～122.9°E) since 2000 are relocated with double difference method.Through analysis to the results,we find that the relocated earthquakes are relevant much closer with faults.The depth of moderate and small earthquakes have regional difference,which is shallower near Changdao(6km in average),but is deeper near the source region of Ms7 event in 1548(13km in average).Combined with seismicity,the earthquake tendency of Changdao area is analyzed.

In this paper,we have introduced the abnormal earthquake activities before Wenchuan M8.0 earthquake in Sichuan Province,such as the earthquake of M>7.7 in mainland of China occurred in grouping feature and the migration of earthquake with M≥7.7 between Sumatra and China-Mongolian border.In accordance with the grouping feature of M≥7.7 earthquake activities,we have pointed out that Wenchuan M8.0 earthquake on May 12,2008 might mark the end of the period of M≥7.7 earthquake activity in Chinese mainland since 2001.However,the earthquake with M=7 may be taken place in Chinese mainland still in the next three years.Based on the characteristics of the seismic activity in specific region,it indicates that the Wen′an M5.1 earthquake on July 4,2006 in Hebei province may be the precursor of the next strong earthquake in North China.

Based on the single scatter model (Aki), using 26 earthquake digital wave data above ML≥2.9 from 2003 to now recorded by Shandong earthquake net, the average Q value of coda in relative region is calculated and relationship between Q value and frequency is discussed. The results are:QC=(313±42)f(0.653±0.145) in sea areas upstate Jiaodong Peninsula;QC=(319±88)f(0.649±0.145) in Jiaodong inland;QC=(259±60)f(0.757±0.277) in Huanghai areas. Contrasting the result with that of other domestic region, the coda scatter feature is that the Q value is higher but dependence on frequency is lower, so it is considered that tectonic activity and seismic activity are low in this region.

The period of historic earthquakes and the characteristic of current earthquake activity in North China area are studied.Through analysis on the characteristic of seismic activity on different belts in North China area in different seismic act we conclude that,North China area is in a modulating stage of fourth active period.It will enter a new seismic active act in a few years,which is active mainly in Yan-Bo belt and east Shandong-south Yellow Sea area with 5～6 magnitude.

The effect of SQIP method on the medium range earthquake prediction in Northern China are reevaluated,the R values calculated by Xu grade criterion are 0.67～0.68 using the retrospective all time-space scan.And the medium-short and short range prediction index of this method is also extracted.The results show that after the anomaly region of synthetical parameter P shrinking about 7 months in average,main earthquake would accure.Among them 53%～54% events accured in 6 months after the shrinking,the 33%～35% events were in 3 months,and a few of events accured after the anomaly region disappeared for 7～8 months.Therefore,the anomaly region of synthetical parameter P shrinking or disappearing can be the medium-short range or short range predicting index for moderate strong earthquake.

The characteristic of history and modern earthquake activities in the Yanshan-Bohai fault zone is studied.We also discuss the temporal and dimensional characteristic of the earthquakes.The result shows that the possibility of earthquake with over M7 is not large,but the possibility of earthquakes with over M6 occurring in the future should not be eliminated.The location in which a medium-strong earthquake may occur will still be in the east of the western and middle parts of the fault zone.The possibility that the next earthquake migrates to the east of the middle part is much.