Abundant magma sources, open magma conduit and high magma temperature are the three major factors that affect volcanic eruption. Meanwhile, topographic condition, lithology of overlying strata and condition of historical volcanic eruptions also restrict the formation of a volcano. Combining the previous researches on Tengchong volcanic cluster and considering the depth of magma chamber, location of fault and magma temperature as the main factors, as well as lithology, strain, stress, volcano distribution density as accessory factors, we set up a model with ArcGis Modelbuilder. Through a series of modeling, analyzing and weighted stack calculating on the basis of classifying all the factors concerned as nine grades according to the risk degree of each factor to the eruption, we finally work out a grading map indicating the potential risk of volcanic eruption in Tengchong region. According to the different colors shown in the map, we can see clearly that the most dangerous area is near the Hehua-Ma'anshan-Shangzhuang Fault. In addition, Qushi-Jiaoshan-Dapotou, Tengchong-Qingshui-Hehua and Wuhe-Tuantian faults are also worth paying attention to. The article provides the theoretical basis for forecast of future volcanic eruption hazard.

Based on WorldView-2 high-resolution satellite image and ASTER GDEM(V1)digital elevation model(DEM)data,the authors studied geomorphological characteristics of the Tengchong volcanic region by means of remote-sensing interpretation,topography-elevation analysis,surficial-slope analysis and terrain-section analysis,with ArcGis and Global Mapper. According to the results of the study,the Tengchong volcanic region has several kinds of geomorphic units which possess corresponding interpretation keys in satellite image,and the latest typical volcanic geomorphic unit can be divided into four categories. Topography-elevation and surficial-slope analysis show that there is obvious difference in surface relief of geomorphic units in the horizontal direction and the geomorphic surface can be vertically divided into four classes. Geographically,the terrain elevation of the basin is higher in west and centre than in east,north and south,which associates with the original landform,tectonic evolution and volcano-magmatic activities. The NS-trending tectonic belts in the study zone controlled the eruption and distribution of the volcanoes. Early pyroclastic volcanoes,such as Daliuchong and Xiaoliuchong,had strong eruption power and shaped towering mountains which cover the middle part of the basin,while the lava-type volcanoes,such as Heikongshan,Dakongshan and Maanshan,with a decreased eruption power,erupted mainly in the form of overflowing lava. On the whole,the structure and evolution of the basin directly controlled and restricted the volcanic activities. At the meantime,the volcanic process transformed the geographic and geomorphic conditions of the basin and shaped the modern volcanic landscape features.

Based on detailed field investigation,three lava flow styles are identified in the Dayingshan,Maanshan and Heikongshan in the volcanic field of Tengchong: pipe flow,inflated flow and laminar flow. Lava flows of Dayingshan are characterized by pipe flow. Heat lost gradually increased from the core to the edge of the flow pipe,resulting in lava consolidating gradually from the surface to the core. Lava of Maanshan is dominated by plane pahoehoe inflated by aa. The lava,in high temperature,was inflated into the lava tunnel as liquid-gas mixing phase,which generated aa. Heikongshan is featured by typical aa lava flow in the proximal phase and middle phase from the vent. The high-temperature plastic lava carried breccias on its top when advancing in a state of laminar flow,forming typical aa lava flow sections with breccias on the top and bottom and dense lava in the middle. In the distal phase,the lava flow formed numerous strip-shaped uplifts of breccias.

Keluo volcanic cluster, which covers an area of ca. 350km², is located between the Greater Khingan Mountains and the Songnen Plain, Heilongjiang Province, and in the north of the famous Wudalianchi volcanic cluster. Twenty-three Cenozoic volcanoes that primarily consist of alkaline basalts are distributed along the Keluo River. The activities and distribution of this volcanic cluster are largely controlled by the regional basement faults, and consistent with the special tectonic setting of NE-trending fault basin. The Strombolian-type central eruption is the predominant eruptive type in this area. Volcanic activities in this area can be divided into three periods, namely, Pliocene period, Pleistocene period and Holocene period. During the Pliocene, a series of central-overflow-type volcanoes, which situated on the edge of the basin, were formed along the NE-trending faults. However, except for some shield lava platforms, most of the original volcanic geomorphic features have been destroyed by weathering. The volcanic activities of early Pleistocene were relatively quiet. But the eruption activities of the Mid- and Late-Pleistocene were also controlled by the NE-trending basement faults, and the eruptive center, type and intensity were all changed as well. These volcanoes are mainly composed of alkali-basaltic scoria cones and lavas. The Holocene volcanoes, as represented by Nanshan, have similar eruptive type and composition to the former ones, but their volcanic structures are well preserved. Some micro-morphological characteristics can be easily recognized at their outcrops. On the whole, the lava covered the former sedimentary strata and changed the river flows attributed to the volcanic activities of Keluo volcanic cluster, as a result, the original geomorphy in the basin was totally altered.

From May 4 to May 30,2011,a field exploration on Ashikule Basin in Western Kunlun mountain area was conducted by the research team from Institute of Geology,China Earthquake Administration and Xinjiang Earthquake Administration.This work is financially supported by the special fund for China earthquake research project "The comprehensive scientific exploration of Yutian M_S 7.3 earthquake in 2008 and Ashikule volcano group".Through detailed field survey on geological and geomopholoical features of Ashikule volcano group,which is one of the volcanic plateaus at the highest altitude(about 5,000m)in the world,we found out the total number of volcanoes,the eruption type and structural parameters,and the active history of the volcano group.Our studies have provided field evidences for resolving the controversies existing in the past,such as the authenticity of the news report about the eruption event on May 27,1951,the eruption pattern of Daheishan volcano,and the reality of Gaotaishan volcano and etc.

The friction behavior of faulted granite samples, with size of Φ 20 mm×40mm and saw-cut at an angle of 35° to σ₁ axis, was experimentally studied under various water containing conditions and tri axial compression. The stability during stable sliding or stick-slip was emphasized. Three types of polished fault surface are considered:(1)two surfaces contact directly without any gouge in between, used to simulate the friction behavior of brittle fault;(2)the preset fault is filled with 0.25g quartz powder with mean grain size of 10μm, used to simulate the friction behavior of a fault containing brittle gouge;(3)the preset fault is filled with 0.25g clay fault gouge with grain size of <10μm, used to simulate the friction behavior of a fault containing ductile gouge. The water content ranges from dry to water saturated, and the pore pressure ranges from 20 to 150MPa. The following conclusions can be drawn from the results of the experiment:(1)The mode of faulting is strongly influenced by the existence of water. For dry polished surfaces without any gouge, there is a certain range of confining pressure in which stick-slip behavior exists. This range of confining pressure may shrink quickly when water enters and forms pore pressure on sliding surface, i.e. the friction behavior turn to stable sliding. For samples with quartz powder, frictional behavior changes from stable sliding to stick-slip when dry gouge becomes wet, and return to stable sliding again when gouge is saturated and undrained. In this case, there exists also a certain range of confining pressure in which stick-slip behavior exists. For samples with clay gouge, frictional sliding keeps stable under any humidity and pore water pressure.(2)Experimental study also shows that stress drop of stick-slip is dependent on the water content. For samples without gouge, stress drop decreases with increasing water content in rock. For samples with quartz powder gouge, however, stress drop increases quickly at first and then slowly with increasing of water content in gouge under drained condition; under undrained condition, stress drop is small at first, then gets larger, and becomes small again when the content of water in gouge increases. When the samples are loaded with pore water pressure, frictional sliding turns to stable and the stress drop tends to zero.(3)Water influences the velocity dependence of frictional sliding of the tested rock samples. The velocity dependence of samples without gouge is velocity weakening at any water content. For the samples filled with quartz powder, it is velocity weakening when the water content ranges from dry to wet, i.e. at different humidity, and becomes velocity strengthening when pore pressure exists on the fault; for the samples filled with clay fault gauge, it is always velocity strengthening.(4)Based on velocity weakening model of friction instability and by considering the order of fault zone from no any gouge, to containing quartz powder gouge and clay gouge as a transition from brittle to ductile regimes, a conceptional model has been established for the relationship between the stability of faulting and the influential factors including fault property, water content and confining pressure(depth). Brittle fault displays velocity weakening in most cases of various water contents, and stick-slip appears in the region of low water content, while stable sliding appears when the water content becomes high(high pore pressure). Semi brittle or semi ductile fault displays velocity weakening when water content is relatively low, and stick-slip may exist; but it will displays velocity strengthening when high pore pressure appears, and the sliding will be stable. Ductile fault always displays velocity strengthening at any water content, and the sliding is always stable.(5)A conclusion can be drawn from the experimental results of this study in the light of pore pressure theory: Entering of water will decrease the stability of the fault system but the existence of water may increase its stability; the former effect can be called“mechanical effet of waster” and the latter can be called“chemical effet of waster”.These are two important aspects when we con-cider the influence of water or fluids on the stability of fault or rock mass. The ranges of confining pressure and pore pressure adopted in this study are comparable with the geological condition from ground surface to a depth of about 6km.Wester appears as free waster in this depth range. Therefore, these experimental results may provide an insight into the geological phenomena in shallow part of the crust the mechanisms and prediction of earthquakes and geological engineering problems etc. For example, it can be used as the criteria of the effect of water on fault stability in numerical simulation of seismic activity, and can also used for analyzing the mechanism and activity of reservoi,induced earthquake. Some reservoi,induced earthquakes show that earthquake activity occurs only at the beginning of waster storage or during the storaging period, then it becomes less and less. Accarding to the results of this study, the former one is dueto the“mechanical effect of water”,and the latter is dueto the“chemical effect of waster”.

The tectonic stress field and seismic tectonics in the Sichuan-Yunnan rhombic block and its adjacent areas are investigated in terms of the "plastic-flow network and multi-layered tectonic deformation" model for continental dynamics(for short, called "netlike plastic-flow" model or NPF model). According to the model, it is presented that in consideration of the transition of deformation regime from brittle to ductile with increasing depth, the lithosphere is divided into several tectonic deformation layers, i.e. the ductile lower lithosphere(including the lower crust and lithospheric mantle)with netlike plastic-flow and the brittle upper lithosphere(including seismogenic layer and the shallow crust)with shear and tensile fractures, as well as the transitional layers(i.e. low-velocity / high conductivity layers)discontinuously distributed between the two layers; the long range transmission of driving force applying at continental plate boundary is carried out mainly by the netlike plastic-flow in the lower lithosphere, which controls intraplate tectonic stress field, tectonic deformation and seismic activities; the plastic-flow network, which is composed of two families of plastic-flow belts(i.e. ductile shear belts)intersecting each other, can be referred to as a "slip line" network developed under large deformation condition. The previous study indicates that the central eastern Asia plastic-flow network system(CEAs)developed under the compression of the Himalayan driving boundary spreads over a broad area in central eastern Asia. The Sichuan-Yunnan rhombic block is located in the southeastern part of CEAs and includes 6 right handed and 16 left handed plastic-flow belts. Under the control of these plastic-flow belts the large-scale seismic belts and the seismotectonic zones consisting of seismic faults are formed within the overlying seismogenic layer. Most of the seismic faults in this region intersect the relevant seismotectonic zones at angles within the range of -15°～+30°, being longitudinal type faults. The directions of the maximum compressive stresses in the lower lithosphere can be estimated from the lines bisecting conjugate angles of the network. Comparing these directions with those in the seismogenic layer inferred using focal mechanism solutions, it is shown that both of them are identical with each other in general tendency, indicating that the stress field in the upper layer is controlled by that in the lower layer; meanwhile, the directions of the stress vectors in the seismogenic layer tend to deviate to some extent from the general tendency owing to the influences of local factors and estimation errors. The horizontal sliding angle of seismic faults(i.e. the angle included between the directions of the maximum compressive stress and the normal to fault strike)ranges from 36.0° to 78.5°, which are suitable for strike slip. Most of the right handed seismotectonic zones in this region have matured with the apparent maturities Λ ≥0.8(Λ is the ratio of the total length of the segments within seismic fault to that of the related seismic belt), while the Λ values of most of the left handed zones are considerably less than 0.8, called quasi seismotectonic zone, except the Dali Tonghai and Tengchong Jinghong zones which approach to maturing. It is worth noting that the previously active faults may transit to be quiescent, such as the southeastern segment of the Honghe Fault zone, since they deviate from the plastic-flow belts, whereas the new seismotectonic zones may be developed along the plastic-flow belts, such as the Dali Tonghai and Tengchong Jinghong seismotectonic zones. Thus, some boundaries of the rhombic block, such as the Honghe Fault zone, have been probably replaced by new boundaries associated with the plastic-flow belts, and therefore the contemporary "Sichuan-Yunnan rhombic block" can be considered as a tectonic unit defined by some plastic-flow belts of CEAs as its boundaries.

The tectonic stress field and seismic tectonics in the North China region are investigated in terms of the "plastic-flow network and multi-layered tectonic deformation" model for continental dynamics. It is presented in the model that in consideration of the basic state of the transition of deformation regime from brittle to ductile with increase of the depth, the lithosphere is divided into several tectonic deformation layers, i.e. the ductile lower lithosphere (including the lower crust and lithospheric mantle) with netlike plastic-flow and the brittle upper lithosphere (including seismogenic layer and the shallow crust) with shear and tensile fractures, as well as the transitional layers (i.e. low-velocity / high-conductivity layers) discontinuously distributed between those mentioned above; the long-range transmission of driving force applying at continental plate boundary is carried out mainly by the netlike plastic-flow in the lower lithosphere, which controls intraplate tectonic stress field, tectonic deformation and seismic activities; the plastic-flow network, which is composed of two families of plastic-flow belts (i.e. ductile shear belts) intersecting each other, can be referred to as a "slip-line" network developed under large deformation condition. The previous study indicates that the plastic-flow network system developed under the compression at the Himalayan driving boundary spreads over a broad area in central-eastern Asia. The North China region discussed in this paper is located in the northeast part of this network system. The directions of the maximum compressive stresses in the lower lithosphere can be estimated from the lines bisecting conjugate angles of the network. Comparing these directions with those in the seismogenic layer inferred using focal-mechanism solutions, it is shown that both of them are identical with each other in general tendency, indicating that the stress field in the upper layer is controlled by that in the lower layer; meanwhile, the directions of the stress vectors in the seismogenic layer tend to deviate to some extent from the general tendency owing to the influences of local factors and estimation errors. It is emphasized that large-scale seismic belts are in fact a response to and manifestation of the plastic-flow belts in the lower lithosphere, while the large-scale seismotectonic zones in the seismogenic layer and shallow crust are controlled by the underlying plastic-flow belts. There are 6 left-handed and 6 right-handed plastic-flow belts involved in the region studied and, correspondingly, the seismotectonic zones upon them are progressively developing with different apparent maturity, Λ, i.e. the ratio of the length occupied by seismic faults to the general length of the corresponding segment of the zone. A seismotectonic zone is considered to be "mature" when the Λ-value is greater than or approximate to 0.8, such as the Yuncheng-Datong zone (i.e. Shanxi zone), Luoyang-Sanhe zone (or called Cixian-Xingtai-Sanhe zone) and Zhangjiakou-Penglai zone. On the contrary, the previously-active fault zones may transit to be quiescent since they depart from the plastic-flow belts, such as the Tancheng-Lujiang and Changdong fault zones. The analysis of 6 cases of deep-shallow combinations of seismotectonics indicates that the crossing angles between strikes of seismic faults and shallow faults in the region studied are not greater than 6.3°～8.1°, implying that the former can be inferred roughly from the latter; most of seismic faults cross the related plastic-flow belts with small angles, being the longitudinal-type faults, while a few of seismic faults with large angles, being the lateral-type; the horizontal-sliding angle of seismic faults (i.e. the angle included between the directions of the maximum compressive stress and the normal to fault strike) ranges from 44.2° to 65.7°, which are suitable for strike-slip.

In triaxial compression experiments with solid confining pressure medium, especially under high temperature and high confining pressure condition, after reaching the peak strength the macroscopic geometrical deformation of the sample increases obviously with increasing of differential stress. This will lead to a large difference between the observed stress-strain curve and the actual stress-strain relationship. This false appearance will give rise to the unreasonably high residual stress in the sample. To solve this problem, during the semi-ductile and ductile deformation stage of rock sample under the HT-HP condition, a correction of stress-strain curve has been carried out based on the following three assumptions:1) With increasing of differential stress, the originally columnar rock sample deforms into a barrel-shape body;2) The volume of rock sample remains constant;3) During the deformation process, the upside and downside surfaces of the sample keep their original size and shape. That is, the diameter of the upside and downside surfaces of the barrel-shape body should be equal to that of the original sample. The observation after the experiments shows that the rock sample was shortened and bulged in the middle part. This qualitatively indicates that the above assumptions are reasonable to some extent. The examination by using actual experiment data indicates that the correction method proposed here is of practical significance. This method is also applicable to the correction of the stress-strain curve during the semi-ductile or ductile deformation process under axial compression condition.

Two series of triaxial tests were conducted for investigation of the mechanics of stick slip that occurred at high pressure and low temperature conditions.By the negative stiffness testing which cancels out a portion of compliance of the machine-specimen system,shear stress versus slip curves of granite saw cuts and quartzite shear fractures were obtained under 300MPa confining pressure.The duration of the slip was increased to about 0.5 second which would be otherwise several milli second when loaded by conventional test methodThe process was well recorded by an X-Y recorder whose cut off frequency is 2. 5 Hz.By another test which can reduce the intrinsic machine stiffness to a dislred value,stress drop was found to depend on the value of stiffness while slip distance remains comparable under different stiffness settings.This result is completely different from estimates by conventional friction models,say,the rate and state dependent friction model and slip weakening model.However,the result is similar to that when strength is controlled by geometric constraints of the contacting surfaces as noted by Lockner and Byerlee (1990).

In order to understand relation between earthquake activity and the variation of pore pressure,this work studied the effect of pore pressure rate on the sliding behavior between rock surfaces,with constant normal stresses ranging from 10 to 120MPa. The result shows that,withhigh increasing rate of pore pressure,surfaces with low increasing rate of pore pressure,slidingbehavior was characterized by stable sliding,and there occurred a transition between the twomodes with a moderate increasing rate. The above mentioned result is important in future research on the precursory phenomena ofearthquake and earthquake control.

Marble samples with sizes from ψ20×44mm to ψ90×198mm are deformed in triaxial compression under confining pressures from 10 to 60MPa. The fractal dimension of main fractures is calculated and analysed. D value does not change with sample size when the environment and material conditions are the same, indicating that fracture is of self-similarity. Confining pressure is one of factors affecting D value. As confining pressure increases, D value decreases below 35MPa and increases above 35MPa, suggesting that when fractal geometry of fault traces is analysed in field, the environmental conditions in which the fault is formed and the possible change with depth should be considered.

The experimental study on transient processes of fracture and stick-stip instability shows that both of the stress drop and the displacement rise are not monotonous.They are oscillatory ones with multifrequencies.The SEM observation on fracture surfaces shows that the oscillation led to bilateral or multilateral traces.By combining the experimental results with the phenomena observed from natural fault surface and fault zone,such as slickensides,grooving,steps and abnormal array of subfaults,it has been presented that one of the reasons for the traces which reflect the bilateral or multilateral motions of natural fault may be the instability oscillation of fault from an event (earthquake).In contrast,these phenomena may be indicators as ancient earthquakes.

As welll known,the instability modes of rocks depend on quite a number of factors,such as rock type,fault gouge,temperature,confining pressure,strain rate and liquid media,etc.It is emphasized in the paper that all of them are associated with the plastic components contained in rocks to different extent.The plastic components of rocks are referred to those of minerals which can deform irreversibly under the given geological and physical environment.Triaxial compression tests of intact quartzite,granite,granodiorite,gabbro and basalt under room temperature and confining pressures up to 0.7 GPa indicate that the contents of plastic components in rocks have no obvious effect on the magnitudes of stress drop of sudden instability,but do influence the instability modes.The plastic components filled in the elastic framework of rock affect the elastic behavior of rock specimen on the whole in two aspects: (1)The effective bearing area of specimen and the effective height of reversible deformation part in specimen are reduced and higher stress level is necessary to accumulate enough reversible strain energy for sudden instability; (2) The plastic components,as damping elements,hinder the rebound of elastic framework and higher strain energy is necessary too.

Some Scanning Electron Microscopy (SEM) microtextures have been observed on the products of quartzite from triaxial compression experiments with a confining pressure of 1-5 Kb and a strain rate of 4.4?10^-5/sec.The SEM microtextures resulting from stick-slip are distinguishable from those resulting from steady-state slip.The former shows the characteristics of bashing and shearing fracture or rapid slipping,and the latter demonstrates those associated with rubbing fracture and slow shearing.The SEM mic-rotextures in products from active faults can be compared with those from experiments.It is significant to distinguish between stick-slip and steady-state slip motion of active iaults by using these typical SEM microtextures.

The triaxial compression experiments of dry Zoukoudian granodiorite at temperature up to 700℃ and confining pressure up to 7 kb with solid confining media,the microscopic observations to the tested specimens,and the theoretical analyses indicate that both shear fracture and frictional sliding have a similar pregnancy process and generation mechanism.The pregnancy process of major shear fracture in a specimen can be divided into three stages: (1) microfracturing with plastic deformation of soft mineral grains; (2) appearance and propagation of macroscopic shear fracture and formation of rock bridges between them; (3) failure of rock bridges and final occurance of the major shear fracture running obliquely through the specimen.Fracturing-through shear strength is a special kind of frictional strength,which characterizes the friction behavior of the nei sliding surface in the originally intact rock specimen.Both shear fracture and frictional sliding can be classified into two types: the gradual and sudden one.Sudden frictional sliding is the stick-slip along pre-existing fault while sudden shear fracture is the "first stick-slip" of intact rock.The confining pressure condition neccessary for the "first stick-slip" and the closely subsequent one is basically the same,which is about 5 kb or higher at the room temperature and increases with temperature.However,it is possible to induce stick-slip under confining pressure far less than 5 kb for pre-existing flat faults which have undergone a quite long sliding distance or a certain change in the orientation of stress field.The upper temperature limit of stick-slip is about 300-350℃ and the lower confining pressure limit of stick-slip is less than 1 kb for dry Zoukoudian granodiorite.In consideration of little possibility for strong earthquakes caused by shear fracture of intact rock owing to the increase of crustal temperature with depth,the principal shock-generation mode for most of strong shallow earthquakes may be the stick-slip along pre-existing faults.

The results of the triaxial compression tests with solid confining pressure media and the theoretical analyses show that the "environmental stiffness",including the stiffness of both axial and confining pressure systems,is an important factor which influences the stress drop. Under the condition of triaxial compression tests the axial stress drop is a hyperbolical function of the stiffness of confining pressure system,and the former decreases with increasing the later. Thus,the problem,that the experimental stress drop is much greater than that estimated from an earthquake,may be explained.The expression of shear stress drop of hypocenter in the crust is Δτ=2λ((S_s—S_k)+(μ_s—μ_kσ_n.0)where λ is the environmental factor which depends mainly upon the environmental stiffness and the orientation of stress field. The values of the environmental factor may be 0-0.9 for the conditions without obvious change in the magnitude of normal pressure and the orientation of principal stresses.The environmental stiffness not only influences the magnitude of stress drop,but also determines whether the sudden stress drop will occur or not. Fully taking account of the effect of environmental stiffness and other factors such as temperature,confining pressure,pore pressure,orientation of stress field,fault materials,etc.,it will finally be possible to recognize the total law of stress drop in hypocenter.It is also indicated in this paper that the direct shear tests and triaxial compression tests with gas or liquid confining media can only model the pressure condition of hypocenter,but cannot reflect completely the "environmental stiffness" which can be controlled to a large extent with solid confining media as presented.

A study on pressure calibration of a triaxial testing apparatus with solid confining media is presented with temperature up to 625℃ and confining pressure up to 6.5kb. The solid confining media used were Pb,AgCl and Nacl. For room temperature, phase-transition materials, such as NH₄I, phenol, AgI, NH₄F and KNO₂ were used to establish the relationship between the pressure applied on the specimen and the nominal pressurre measured outside The vessel. The correction of confining pressure △σ_c changing inversly with temperature was determined quantitatively by the "temperatueeffect" tests. It is shown that the pressure transmitting behavior of NaCl is obviously improved above 200℃ and a semi-emperical expression for △σ_c was derived for NaCl as a function of temperature T(℃), i. e. △σ_c = (0.491 + 0.000650T) [2.325-0.455 (T-25)^0.217].