The Lixian Luojiapu fault zone shows clear activity since the late Pleistocene. The Holocene strata are directly offset in the Lixian-Luojiapu and Tianshuizhen-Jiezikou segments. Surface scarps are easily to be found and the gullies are sinistrally offset along the fault. Considering the widely distributed earthquake slope slides and liquifaction, it is suggested that the Lixian Luojiapu fault zone is the seismogenic structure of the 1654 Tianshui M8 earthquake. The average horizontal and vertical slip rates are 0.95mm/a and 0.35mm/a, respectively since late Pleistocene. The ratio of vertical slip rate to horizontal slip rate is about 1/3, which is about the same as the ratio between the vertical and horizontal displacement in an event.

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 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 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.

The 4 paleoearthquake events that have occurred on seismogenic fault of 1679 Sanhe Pinggu M8 Earthquake since 20ka B.P. are exposed through the analysis of trenches and fault scarp profiles. The earlier two events are marked by liquefaction and the later two events are shown by direct fault offset,including the 1679 event. The 1679 event and pre 1679 event are two characteristic earthquakes of which the maximum displacement is about 1.75m and 1.41m,respectively and the intensity of two events is very close. The occurrence time of 4 events was about 20000,13000,7500 and 317a B.P.,respectively. Average interval of recurrence is (6561?691)a. It indicates the characteristics of quasi- periodic occurrence of earthquakes.

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.

Fault gouges record a great deal of information on fault activity. Preferred orientation and fabric of minerals have close relation to the mode of slip along the fault. In this paper,the illite fabric in the Xiangshan Tiangjingshan fault zone is determined by using the X-ray method with Textrete-Goniometer. Our results indicate that the illite fabric in the middle sgement has no preferred orientation and it is the result of stick-slip of the fault,while that in the east and west segments has maximum density areas and it is caused by the sinistral shear creep-slip of the fault.

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.

Geological evidence indicates that the fault activity on the middle segment (Dali and its adjacent region) is the strongest along the Honghe fault (the Red River Fault).The active fault shows a distinct tendency of getting younger from the ends to the middle segment of the fault,i.e,faulting in the Dali area is the youngest,which coincides with the distribution of recent strong shocks.Geological evidence and its ages show that five events with a recurrence interval 昽f about 1500 years occurred in the middle-late Holocene time,presumably associated with an earthquake of M=8.

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.

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.

The similarity in the seismogenic structure, rupture mode and the focal stress field indicates that the earthquake of magnitude 6.0 occurred in Haicheng on May, 18, 1978 can be regarded as a strong aftershock of the 1975 Haicheng earthquake with magnitude 7.3. After main earthquake there have not been intensive activities of aftershocks. But they toke place much later, it may be explained by the disrupture of the locked section of NNE running active structure.The authors of this paper re,fer the strong shocks taken place within 10 years after the main shock to be the late strong aftershocks. By the synthetic analysis of the geotectonic features and the nature of the whole seismic activity series of the Haicheng earthquake, it is shown that the multi-locking structures must be a necessary background and the locations for generating the late strong aftershocks. Its anomalous precursory, however, was less obvious and appeared only along the direction obliquely aerossing the principal structure in area concerned. Some characteristics of the late strong aftershocks and relevant strike-slip mechanism are slao discussed herein.

Based upon the studies of Late Cenozoic faulting and its related features in connection with the data of seismological observations involving a part of focal mechanism, topographic changes and geophysical explorations of the deep portion of the earth, the principal characteristics of the Late Cenozoic tectonic stress field in the region studied are discussed in this paper. It is suggested that the Himalayan movement together with the underthrusting of the Pacific plate reformed the regional stress field -of North China from Late Mesozoic to Early Cenozoic. As a result, the horizontal NEE-SWW trending compression is predominant. The change of the principal compressional stress from NEE to SEE in direction indicates both the consistancy between the stress fields of the region under investigation and North China area and also the difference in their individual features. Presumably the collision of the dominating Indian plate with the Eurasian plate and the underthrusting against one another by compression of the Pacific plate, together with a NW running underthrusting of the Philippines Sea plate and the lateral spreading of the surface crust caused by the upwarping of the upper mantle were responsible for this complex situation.