We have conducted an integrated survey and investigation on the Quaternary activity of the Liaocheng-Lankao buried fault. The used methods include geochemical exploration, shallow seismic exploration, drilling geological profile and neo-strata dating. The object is to determine the accurate location of the fault, dislocation amount of each time period since Quaternary and the offset age of the last time of dislocation. The results show that the dislocation of the fault extends upward to the depth 20m or so below the surface. This fault has been active in early Holocene time. The average slip rate of the fault is 0.12mm/a.

The Longling-Lancang fault zone is a newly emerging fault zone, which is composed of multisecondary faults, distributed in the obligate or clustered types, and characterized by the zoning of active faults, earthquake faults and earthquakes. Its kinematic feature is dextral extensive and the formation epoch is early-middle Pleistocene. It is still active in the later period. The rupture in the future tends to cut across the tectonically-blocked segment, discontinuous segment of the fault and then through the whole fault zone. The formation of the nealy emerging fault zone has close relation with the uplift of the Qingzang Plateau. The composite action by the material fluid from the north to the south and the intrusion of Asamu block towards northeast makes the Dianmian block to rotate in a counter-clock wise direction and forms a new dextral shear, NNW-trending fault zone in the central area of the block.

Based on new data and studies on active blocks in recent years, we propose the principle, evidence and method for division of active blocks of the south region of Sichuan Yunnan Province. It is suggested that the Quaternary active faults which have major scales and have been active till present are the necessary and primary boundary conditions for block division. The newly formed Tengchong-Jinghong NNW zone and Dali-Chuxiong NWW zone have an important role in the block division. In the light of the nature of faults, motion modes, and GPS data the present-day active mode of each block is analyzed. It is concluded that earthquakes of M 7 or greater occur on the first class boundaries of active blocks, events of M6～M7 on the second class boundaries, and the active blocks of secondary class are the main locations of major earthquakes.

Based on the crustal depth, gravity-magnetic feature, active faults in late-Quaternary, geomorphic variance, fault-depression basins and the difference of seismicity, the studied region is divided into first and second grade blocks. There are 7 first grade blocks and 33 second grade blocks. The shapes of the first grade blocks are mostly elongate in plane and trapezoid or up-down trapezoid in the section, and some are polygon or triangle. The shapes of the second blocks are mostly rhombus, thrust-type in the section, and some are elongate or triangle. The main motion types include:horizontal thrusting, vertical lifting or depressing, and flow-extending and rotation. The block motion is controlled by the mechanism of crust "contract-escaping-rotation". That is, when the crust block is exerted by extruding stress, the intense contraction happens. Then the crustal block lifts and escapes towards the east. The block rotation appears in the process. The result is of great importance for "high resolution observation of geo-deformation and earthquake prediction".

Based on the gradation of stream and ridge offset and the dating of terrace sediments in a distance of 150km from Hongyaza in the west of Akesai eastward to Subei and Hongliuxiakou, the river offsets in Quaternary can be divided into 8 grades and their formation dates are acquired. The fault slip rates in different segments range 4.7～6.7mm/a. The average value is 6.0mm/a. As to the local section in a short period, the maximum slip rate can be 7.7mm/a. The distribution of offsets and slip rates shows that they are large at the middle and small at the ends, which may demonstrates that rupture initiates from the middle and develops towards the ends. The slip rate in Pliocene is larger than other epoches, which may be related to the quick lifting of Qinghai-Tibetan block since 5Ma B.P. and the large scale of escaping. Data show that fault rupture begins at the main fault, then extends to the vicinity and goes back the main fault.

The mode of slipping along the eastern Liupanshan piedmont fault zone is analyzed through both macroscopic and microscopic investigations. The results show that (1)this fault zone can be divided into north,middle and south three segments based on the characteristics of the fabric from fault gouge. This is consistent with the result from macroscopic along the fault zone in recent years.(2)local strong deformation, traction fold, Riedel shears angle (R₁) being in the range of 11°～26°, P foliation and randomly preferred orientation of illite mineral that developed within the fault gouge are indication of stick slip and left lateral strike-slip along the north segment.(3)general deformation, Riedel shears being at angle of 11°or less, banded foled, ptygmatic structure and polygemic preferred orientation of illite mineral that developed within the fault gouges are the indicators of creep slip and reverse slip along the middle and south segments.

New results of field investigations show that the eastern Liupanshan piedmond fault is an active reverse fault zone since late Quaternary. This fault zone can be divided into north,middle,and south three segments in the light of the changes of its strike,active ages and active natures. The north segment is dominated by left lateral strike slip,while the middle and the south segments are characterized by thrust movement. The active age of the north segment is youger than the south and larger horizontal dislocations occurred on the north. Such changes of fault activities since late Quaterary are associated with obstruction for the eastward slide of the Xihuashan Liupanshan block as well as the variation of the fault strike.

The Longling earthquake of M7.3 and M7.4 in 1976 and the Lancang Gengma earthquake of M7.2 and M7.6 in 1988 are two typical double main shocks occured in Longlin Lancang fault zone,Yunnan. Based on the seismicity analysis of the events,it is found that they have different characters. The Longling earthquake occurred in a block which composed mainly of the granite in which the structure is comparatively homogeneous. The focus machanism analyses of the Longling earthquake give the direction of compressive stress in NNW,the trace lines of the principle stress axis extends mainly in SN to NE. The direction of the seismogenic structures are in NNW to SN and NE to NEE. There are two intensity areas of 9 degree of which the long axes are nearly right crossed each other. The Lancang Gengma earthquake occured near an ancient plate boundary with complex seismotectonic background. The directions of principal compressive stress of the two main shocks given by focal mechanism analyses are different. The Gengma M7.2 earthquak occurred in an area in which the tectonic stress is mainly tensional in NW direction. While the principal compressive stress field of the Longling M7.6 earthquake is characterized by the fan shape in NS direction. The seismogenic structures of the Langcang Gengma earthquakes are of en echelon in NW direction. The axes of meizoseismic areas of two main shocks are parallel each other. Based on the comparison and analysis,the X-type model and triggering model of seismic rupturing for the double main shocks are proposed,and their features and formative condition are also disscussed.

The Altun structure system is a structure domain that consists of a set of monomict structures which have consistent strike, slimiar active character and origin connection. Many different geological units and a series of approximately parallel faults are involved in the Altun structure system. In the Altun structure system, all faults have sinistral displacement. Since Oligocene Miocene, sinistral displacement and slip rate for the the Altun structure system are 450～700km (average displacement is 580km) and 15mm/a, respectively. In the same period, displacement in the Altun fault zone is about 225～375km (average value is 300km), the left lateral slip rate is about 7mm/a. The displacement and slip rate for other faults in the Altun structure system are 150～250km (average displacement is about 200km) and 5mm/a, respectively. Since Pliocene, sinistral displacement and slip rate are 90～130km (average displacement is about 110km) and 11mm/a, respectively. For the Altun fault zone, left lateral displacement and slip rate are 50～80km (average is about 65km) and 6～7mm/a, respectively. For the other faults in the Altun structure system, sinistral displacement and slip rate are 40～50km (average is 45km) and 4mm/a, respectively. Since Quaternary, sinistral displacement and slip rate are 20～27km (average is 23.5km) and 9～12mm/a, respectively,. For the Altun fault zone, left lateral displacement and slip rate are 7～17km (average is 12km) and 5～7mm/a, respectively. For the other faults in the Altun structure system, left lateral displacement and slip rate are about 10km and 4～5mm/a, respectively. From Oligocene to Quaternary, the left lateral slip rate of the Altun structure system and the faults in system became slow down. The left slip rates get smaller from south to north. For the Altun fault zone, the displacment in the middle segment is larger than the two sides in Quaternary. It means that the left displacement reduced from the middle to two sides of the Altun fault zone.

Since Quaternary,intense activity has occurred along the Honghe fault zone. But its active features in intension,time and form are differential on the different segments of this fault zone. Based on the studies of predecessors,combined with features of tectonic geomorphology,composition of fault materials and a large amount of dating data of strata associated with fault activity,the activity characteristics of the fault and its time-space evolution since Quaternary have been studied synthetically for the whole fault zone. The results are: (1) As time goes on,the active center removed gradually from southern to northern segment of the Honghe fault zone,the acitve sites in later Holocene is located near Dali City and Midu county. (2) The active property of the fault zone is different in basins and mountain areas on the same secondary fault,the former is dominant with dip-slip and the later is dominant with right-lateral strike-slip movement. And their activity time is not synchronous too,the active age of former is often newer than the later. (3) On the same segment of the Honghe fault zone,the active ages of range front-fault of the Ailaoshan trend to be older than the Zhonggu fault and removes gradually from the former towards the later.

Since Quaternary,large-scale right-lateral movement has occurred along the Honghe fault.It leads to mass loss and results in extensional area at the tip of the northern segment of the fault.In spatial distribution the strike-slip segment and the extensional area are correlated each otherand belong to a system.The direct evidence for strike-slip of the fault includes a number of phenomena such as linear geomorphic feature,steep fault plane,nearly horizortal fault scratch,and water-system offset.The extensional area is indicated by the en echelon normal faults,basins,turns and branches of the fault end which were developed on the northern segment of the Honghe fault.The activity of the strike-slip segment and fractures and basins in the extensional area is synchronous and occurred in Quaternary.The right-lateral strike-slip occurring along the strikeslip segment of the fault is about 7.1km,which was transformed into the extensional area at the end of the fault associated with the block motion.The amount of extension in the right-lateral direction of the extensional area is about 5.35km,comparable to the strike-slip movement.Therefore the genetic relationship between the two types of tectonic deformation has been confirmed quantitatively.

The process of the upward propagation and extension of deep-seated reverse fault is an attractive research topic. Based on the analysis of practical data, it is found that there are fourtypes of the attenuated upward fracture propagation of reverse fault in shallow loose deposits.They are the branching of the terminal portion of the fault,the transformation of the fault intofold, the thinning out of the fault in loose deposits, and the disturbance and deformation of thedetrital materials ahead of the reverse fault. The branching of the terminal portion of the faultand the disturbance of detrital may be related to an abrupt seismic dislocation event,while theother two types can be attributed to attenuation in elastic-plastic transition regime.

The study of regenerated microstructures of fault gouge formed under triaxial friction experiment and natural gouges indicates a certain relationship between microstructure features and fault slip mode.The samples subject to stable slip exhibits the fault gouge to be uniformly deformed,resulting in low Riedel shear angles(<14?)and cataclastic flow structure. When the samples were subject to stick slip,the fault gouge was locally stronglydeformed,and random cracks were formed at a high Riedel shear angle(>14?).The regenerated microstruc-tures in natural fault gouge zones may also surves as a potential tool for identifing paleoearthquakes.

Qilianshan active fault zone is situated in the northeastern border of Tibet Plateau.It con-sists of North Qilianshan fault and Haiyuan fault. It is mainly a compressive-sheared and sinis-tral-slipping fault zone,its slip rate at most up to 9mm/a。Many ancient earthquakes and histori-cal earthquakes occurred in the zone.On the basis of the active behavior of the fault zone,three sections and seventeen segments were divided.According to the relation of ancient earthquakes,slip rate and length of segrnents,a bivariate regreession model was set up. The evalution of risk was made. Finally,we can disfinguish between three risk segments of type A and four risk seg-ments of type B.

Displacement rale along the Honghe River fault (northern segment) since Pleistocene was determined in this paper on the basis of geological investigation:for the narrow valley segment (Dingxiling),offset rate is 8mm/yr,and the throw rate is 1.8mm/yr;for wide one (Dali),5mm/yr and 9mm/yr,respectively.It can be estimated from the parameters of fault displacement that recurrence intervals for M6,8 earthquake are 178?29 years.It is consistent with the recurrence intervals (150?50 years) of M 6-7 earthquakes from historic seismic records in this area.It may be useful to immediate-long term earthquake prediction.

The comprehensive characteristics of active faults,physical mechanism of fault basins,pole direction of drainage system and fault plane solution of moderate and small earthquakes indicate that recent tectonic stress fields in the study area trend from NNW to nearly SN.It follows that local tectonic stress fields in the area is related to the tectonic deformation of upper crust,caused by slipping to the south of Sichuan-Yunnan block in which the fault basin in the area has been a pull-apart basin of the surface crust since the Neogene.The boundary faults of the basins tend to be in the form of the shovel and to be down to at a depth of 1-2 km,and moderate/small earthquakes are concentrated at a depth less than 20 km,which suggests a strain release of two sorts at different depths in the slipping process.It is possible that the lower part of the crust is in the process of being deformed to northeast between the large-scele platas.Earthquakes of >M 6 with characteristic of high-angla strik-slip mainly concetate at a depth of 20-25 km which is partly related to NE compressive stress.The intersection of large-scale and local stress fields may be representative of tectonic stress at different depths.Of course,the Hounghuo River fault zone in the presence of shear-tension obviously has an effect on shifting of the stress field direction of this region.

Since the Late Pleistocene,the movement of the northern segment of the Honghe fault zone has been different from that of the southern one.At the southern segment movement is primarily characteristic of single right-lateral shearing,whereas at the northern segment,of a compositive right-lateral shearing with faulted-depressional extension.With in the compositive zone in question appears an en-echolon fault pattern due to alternate shearing and fault-depression.From the southeast to the northwest,they are: Ding Xiling shearing zone,Dali fault-depression,Xiashankou shearing zone,Eryuan fault-depression,Cibihu Lake shearing zone and Jianchuan fault-depression.Geomorphic feature of shear zone and fault-depression is completely different,the former appearing as a narrow valley and the latter,as a basin.This paper is focused on the determination of displacement rates and recurrence intervals of earthquakes of Dixiling shear zone and Dali fault-depression having remained since the late stages of Late Pleistocene.For Dixiling shearing zone,right-lateral displacement rate is 8mm/yr,and vertical slip rate is 1.8mm/yr,with a ratio of 4:1 and for Dili fault-depression,5mm/yr and 9mm/yr,respectively,with a ratio of nearly 1:2.According to calculations of the parameters of fault displacement,we have found that recurrence intervals for magnitude 6.8 earthquake are 178±29 years.It is consistent with the recurrence interval (150±50 years)of M 6—7 earthquakes from historic seismic records in this area.It may be useful to immediate—long term earthquake prediction.

Basing upon the recent field investigations, the principal features of the NW trending fault structure in Yanshan region are summarized in this paper.By analyzing structural, seismological and geophysical data, the authors demonstrated the space distribution, formation, development and movement mode of the NWW trending basement fault zones, as well as their relation to the seismicity. It is suggested that the NWW trending fault zone can be attributed to a crustal fault, controlling both the development of fault block structure and the recent seismicity. The fact that the NW faults spread en echelon and cluster into a zone is a indication of a NWW fault zone in the superficial strata. Moreover, the movement mode of the zone under investigation has a very close relation with the relative motion of the fault block structures. Since Mesozoic and Cenozoic periods, in addition to the differential movement, this fault zone was of shearing motion which had a very obvious changes in nature during the periods from Late Cretaceous to Early Tertiary.

The Ninghe earthquake of magnitude 6.9 (1976, Nov. 15) can be regarded as a continuation of the Tangshan earthquake of magnitude 7.8 (1976, July 28). The latter was resulted from the action of the NEE trending compressive stress on the interlockingportion of the NE trending Tangshan fault zone. The seismogenetic structure concerned shows itself as a kind of asymmetric bilateral rupture. A new stress-concentrated area occurred, when the rupture spreads toward south-west and intersected the NW and NWW trending faults in the vicinity of Ninghe. This area under study was once more subjected to fracturing under the action of the NEE trending compressive stress leading to the occurrence of an earthquake of magnitude 6.9.The main fracture plane caused by the Ninghe earthquake still lies within the NE trending Tangshan fault zone inducing the sinistral slip of the NW trending fault. It was, therefore, a consequent of a simultaneous fracturing of the conjugate faults.Comparing and analysing the seismogenetic structure and the fissures, focal mechanism and the characteristics of the aftershock sequences of both the Ninghe and the Tangshan earthquakes it is suggested that the two earthquakes are tectonically related and expressed as main shock-aftershock relationship. This characteristic may serve as a clues to predict the strong aftershocks. It is found that after a main shock the aftershocks were mostly distributed along the trend of the main fracture zone, whereas strong aftershocks usually occurred at the locking portion of a transverse structure.