The reconstruct of the stick-slip and creep histories is essential for understanding fault activities and seismic hazard assessment. Distinguishing stick-slip and creep using geodetic technology has become a hot research area in recent years, but distinguishing and estimating seismic slip and creep on geological timescales(e.g., over hundreds of years)is challenging due to the lack of historical, geodetic and remote sensing data extending back more than a few hundred years. This study uses a newly developed dating technique(rock surface optically-stimulated-luminescence(OSL)dating)combined with the OSL decay parameters of granite samples from the Langshan fault in Inner Mongolia to simulate optically stimulated OSL-depth curves and depths of half saturation of luminescence signal under various scenarios such as fault seismic slipping, creeping, and erosion of colluvial wedge. The study compares these OSL-depth profiles, especially the depths of the half saturation, under different slipping modes, and summarizes their features.

During fault seismic slip, samples at different heights along the fault scarp display a “step-like” distribution pattern at their depths of half saturation. While during creep, however, they exhibit a “slope-like” pattern. Such differences may lie in that the slope during accelerating creeping is steeper than the slope during constant-speed creeping. Correspondingly, the resolution of residual luminescence-depth profile and depth of half saturation is also higher during accelerating creeping. During intra-earthquake creep events between seismic slip occurrences on the bedrock fault scarp, the distribution of half-saturation depth in the samples includes segments resembling both “steps” and “slopes”, which indicate the seismic slip and creep activities of the fault respectively. If the samples at the base of the colluvial wedge have had a sufficiently long last exposure time, the luminescence-depth profile and half-saturation depth distribution due to the erosion of the colluvial wedge would be approximately the same as in the three-phase seismic slip scenario. This indicates that samples previously buried by the colluvial wedge may be considered within the seismic displacement. Conversely, if the last exposure time of the base samples at the base of the colluvial wedge is short, the bleaching depth of the luminescence signal of these base samples will be noticeably shallower than that of the other samples within the seismic displacement, indicating the observed erosion of the colluvial wedge in this case. Furthermore, the seismic displacement ideally should include the buried location of the colluvial wedge. Therefore, when the luminescence curves and half-saturation depth distributions fail to identify the presence of the colluvial wedge, it is acceptable to include the buried location of the colluvial wedge in the seismic displacement calculation. Conversely, the luminescence-depth curves and half-saturation depth distributions document the erosion caused by the colluvial wedge. The simulation results demonstrate that this method can effectively distinguish between fault slipping and creeping, obtain corresponding displacements, and potentially record the erosion of colluvial wedge.

This study also analyzes the temporal resolution of the method for distinguishing fault activity times and the spatial resolution for quantifying displacements. The specific situation is as follows. When exposure age of the bedrock fault scarp is within a thousand years, the rock surface OSL dating method can easily distinguish types of active slips and seismic displacements for the earthquakes with a recurrence interval of hundreds of years. When exposure age of the bedrock fault scarp is in the range of 10⁰-10¹ka, the method can easily distinguish types of active slips and seismic displacements for the earthquakes with a recurrence interval exceeding a thousand years. When exposure age of the bedrock fault scarp is over ten-thousand years, the resolution of this method may be significantly reduced. The spatial resolution of seismic displacements using this method depends on interval between sampling and testing samples, typically in 10~30cm.

Phytoliths have shown a lot of advantages in dating due to their widespread distribution, structural stability, and preservation integrity, especially since phytolith carbon was used in radiocarbon dating. However, there is a problem of overestimation of phytolith carbon ¹⁴C ages, which may be due to its structure destruction during pre-treatment processes of the rapid oxidation and high temperature. It is necessary to identify the subtle changes in its structure under high-temperature conditions based on its chemical composition and certain physical properties. As a special amorphous hydrated SiO₂, using their luminescence signals for thermoluminescence(TL)or optically stimulated luminescence(OSL)dating can be directly compared with their ¹⁴C ages even as an alternative dating method, and the luminescence property changes of phytoliths may have a reference value for identifying the physical structure changes. In this paper, modern phytolith samples extracted from dry rice straw were taken as an example to study the stability of OSL and isothermal TL(ITL)signals. We conducted a series of conditional experiments to determine the specific experimental process of OSL and ITL₁₆₅ signals, and discussed the feasibility and reliability of the dose-signal response relationship and test process under different given doses of dose recovery experiments. Moreover, the OSL signal were tested by a conventional single-aliquot regenerative-dose(SAR)protocol which firstly preheated at 200℃/180℃ to remove the instability signal and then blue excited at 125℃. The OSL signal of phytolith sample rapidly decays under blue light and is basically reset within 5s of excitation. The sensitivity corrected OSL signal intensity and regeneration dose can respond one by one and a growth curve can be established, indicating that there is also a trap structure within the phytolith particles that can generate relatively stable OSL signals. However, there are still some problems which need further to be solved such as relatively weak signal intensity and poor sensitivity. The results of bleaching experiment show that the OSL signal intensity of phytolith particles decays exponentially under sunlight, and the OSL signal irradiated by given dose of 85Gy can be bleached about 90%within 100s and bleached completely around 800s, which suggests that the phytolith samples have good sunlight bleaching susceptibility. There is a stable and easily bleached OSL signal in natural phytolith particles, however, the experimental procedure is only suitable for samples with lower given doses(below about 200Gy)and the dose recovery rate of older samples is lower. On the other hand, 425℃ TL peaks were found in the ITL₅₀₀ curves of phytolith at both a higher given dose(850Gy)and a lower given dose(85Gy), but they could not be used for dating because of instability. There was a remarkble and stable TL peak at 165℃ under a higher given dose(850Gy). The relatively stable ITL₁₆₅ signal has the potential to be used in dating research and its experimental procedure is also by SAR method. The dose recovery rate of ITL₁₆₅ signal under different given doses(above about 50Gy)was in the range of 0.8-1.2. Both OSL and ITL₁₆₅ signals have the potential to be used in dating studies but need to be tested with samples of known-age. The characteristic dose D₀ of OSL and ITL₁₆₅ signals of phytoliths are(326.8±19.5)Gy and(504.9±49.9)Gy, which implys that phytoliths have a greater saturation level than quartzes. Meanwhile, the ITL₅₀₀ curve heated at different annealing temperatures has the potential to identify changes in phytolith luminescence properties and physical structure. The structure of phytoliths begins to change at around 300-350℃, and irreversible structural changes have occurred at around 600℃ and gradually become sensitized. This also means that the extraction process of phytoliths using wet ashing rather than dry ashing may destroy the structural integrity of phytoliths and resulting in an overestimation of phytolith carbon AMS ¹⁴C ages. Whether it is by using AMS ¹⁴C dating method or OSL/TL dating method which phytoliths as the main dating material, phytolith particles should not be placed in a high temperature environment above 300℃ at any stage during the experiment in order to avoid irreversible damage to its structure. The luminescence age obtained by the OSL signal and ITL₁₆₅ signal of phytoliths can be compared with the ¹⁴C age to determine whether there exists an overestimation, and if the two ages can be verified, there is no need to use other dating minerals which is of great significance for the dating of precious archaeological materials.

Terrestrial in-situ cosmogenic nuclide dating(TCND)is one of the most important geochronological techniques for the paleoseismic study of bedrock fault scarps, landslides, and rock avalanches. With many target minerals, due to its uncomplicated composition, widespread occurrence, and simple chemical treatment, Quartz has emerged as an ideal dating material for terrestrial in-situ cosmogenic nuclides dating methods, such as ¹⁴C, ¹⁰Be, ²¹Ne, and ²⁶A1. Prior to accelerator mass spectrometry measurement, the separation of pure quartz from field-collected rock samples was a pivotal step in TCND. However, the elevated aluminum content in quartz samples undermines the reliability of TCND results. Generally, most of the aluminum content in samples originates from impurities like feldspar. To ensure accurate dating outcomes, the content of Al in samples should be reduced to less than 200 ppm. Therefore, effective separation of feldspar and quartz in samples and obtaining pure quartz is the first step in TCN dating. The conventional HF/HNO₃ etching method to separate and purify quartz is widely utilized, but it is time-consuming and low-efficiency. Particularly during the HF/HNO₃ etching stage when dealing with granitic samples containing abundant feldspars and mica impurity minerals necessitates repeated treatments to eliminate feldspars completely; this not only increases etching cycles but also leads to sample loss significantly. It has a great impact on the application of in-situ cosmogenic nuclide dating in active tectonics. Consequently, physically separating quartz from samples before chemical purification can effectively shorten the chemical etching duration while the flotation separation method can effectively remove most gangue minerals in quartz and achieve preliminary purification of quartz.

This article presents a laboratory-integrated flotation purification device and proposes enhancements to the conventional quartz etching process in order to improve its purification efficiency. The purification device uses dodecylamine as the collector, hydrofluoric acid as the feldspar activator, nitric acid as the regulator, and eucalyptus oleanol as the foaming agent. The bubbling component within the device provides sufficient carbon dioxide bubbles to float out feldspar and other minerals in the sample reversely. To evaluate its efficacy in flotation separation, enrichment, and purification, this study conducted tests on two commonly encountered bedrock samples of granitic gneiss and quartzite.

Observation results under a stereomicroscope show that the quartz content in the quartz component after floating is more than 90%. The etching results of the whole rock and the floated quartz components show that after etching 2-3 times with HF/HNO₃, the Al concentration can be reduced to less than 200ppm, which fully meets the requirement of cosmogenic nuclide dating. The quartz separated by flotation from cryptocrystalline quartzite samples can also reach the dating requirements after etching 7-8 times.

Compared to direct etching following bulk-rock sample crushing, this approach reduces etching time by over a half, significantly minimizing reagent consumption for HF/HNO₃ etching and thereby enhancing TCND efficiency. The bubbling power section of our flotation device directly introduces carbon dioxide gas into the flotation liquid to increase the bubble content in the slurry. Consequently, there is improved collision and contact between quartz and feldspar particles with bubbles, resulting in enhanced flotation effectiveness. This system can be effectively employed for separating feldspar from other impurity minerals present in gneiss samples. The proposed flotation process in this study is straightforward and user-friendly while allowing flexibility in adjusting sample quantities ranging from tens to hundreds of grams as required. Furthermore, this high-efficiency flotation separation system may offer insights into processing zircon, apatite, and other dating samples.

It is difficult to use traditional trenching and field geological investigation to yield the age of paleoseismic events along active fault in western mountainous areas of China where the geomorphic trace mark and sediments are often eroded or altered by human activities. The recurrence interval of paleoearthquake possesses greater uncertainty. It is necessary to yield ages of paleoearthquake event from different ways and examine the reliability of paleoearthquake results. In these regions, an earthquake with magnitude greater than 7 can produce rock avalanches around 200~400km away from the epicenter, such as the Wenchuan earthquake in 2008, due to their structure setting of strong neotectonic activity and the higher topographic relief. Therefore, the seismic bedrock landslide and rock avalanche can record the occurrence time, intensity and damage of strong earthquake in the mountainous area. This provides a new way to assess the frequency and intensity of paleoearthquake occurring in the intraplate continental areas(such as the north-south seismic zone)where strong earthquakes recurred for hundreds to thousands of years based on the seismic landslide records. Identifying ancient earthquake bedrock collapse relics in Quaternary deposits and accurately determining their ages will not only help broaden the study on the recurrence history of active fault, but also assess the earthquake risk in mountainous area.
As shown by previous studies, the Schmidt-hammer exposure-age dating(SHD)method is a relatively simple, rapid, cheap and non-destructive in-situ exposure age dating method. In this study, ancient earthquake bedrock landslides and rock avalanches with known historical records distributed on the Qinling northern piedmont fault and the Huashan piedmont fault are used to preliminarily establish the rock weathering factor with age calibration curve. The rebound values of rock surface at dozens of sampling sites of each rock avalanche and landslide are measured by Schmidt hammer and analyzed statistically. The weathering factor of the exposed rock of each rock avalanche and landslide is calculated and the solution of SHD method is discussed. The reliability of SHD is evaluated according to the measured data and the records of historical age. The main conclusions are as follows:
(1)The Schmidt hammer rebound value of rock surface at three ancient earthquake bedrock landslides and rock avalanches is negatively correlated with their historical ages. The older the historical record age, the lower the average rebound value of the rock, and vice versa. Based on the statistical analysis of weathering factors of rocks of bedrock landslides and rock avalanches, a preliminary age calibration curve is obtained as T=(19 723±888)×f_w-(2 145±166). This curve can be used to infer the bedrock landslides and rock avalanches of more than 5×10² a BP, and it provides a new relative dating method for the ancient bedrock landslide and rock avalanches within the age of 3 000a BP in the northern margin of the Qinling Mountains.
(2)Under the climatic and lithological conditions of the northern margin of the Qinling Mountains, the relative ages of bedrock landslide and rock avalanches can discriminate the interval of millennium scale according to the rock rebound value measured by Schmidt hammer. However, it cannot distinguish the difference in weathering degree of the bedrock landslide and rock avalanches with the interval of less than 500 years.
(3)The Schmidt hammer rebound value measured repeatedly on fresh rocks shows that the fluctuation range of the rebound values is small, within the value of 0-3, which is helpful to rapidly select qualified sampling sites for terrestrial in-situ cosmogenic nuclide dating(TCND). Thus, the Schmidt hammer value can be used to evaluate whether the rock samples have the problem of nuclide inheritance induced by complex exposure history such as post-exposure and secondary transportation. This would introduce greater objectivity to the sample selection and possibly require less samples, thus reducing the costs; meanwhile, it will improve the dating efficiency and ensure the reliability of TCND. Therefore, SHD method is a valuable complementary method to TCND.
(4)Under the climatic and lithological conditions in the northern margin of the Qinling Mountains, the rebound value decreases by (25%±1%) for rocks after weathering for 2ka, by (16%±1%) for 1ka, and by (15%±1%) for 0.5ka.

The Karakoram Fault is located in the west of the Qinghai-Tibet Plateau and crosses Kashmir, Xinjiang and Tibet in China. It is a large normal dextral strike-slip fault in the middle of the Asian continent. As a boundary fault dividing the Qinghai-Tibet Plateau and the Pamir Plateau-Karakoram Mountains, the Karakoram Fault plays a role in accommodating the collision deformation between the Indian plate and the Eurasian plate and in the tectonic evolution of the western Qinghai-Tibet Plateau. The fault trace in Ngari area is clear and the faulted landforms are obvious, which show strong activity characteristics in late Quaternary. As a large active fault, only one earthquake of magnitude 7 has been recorded on the Karakoram Fault since the recorded history, namely, the Tashkurgan earthquake of 1895 at its north end. There are no records of strong earthquakes of magnitude≥7 along the rest of the fault, and no paleo-seismic research has been carried out. Ages of recent strong earthquake activity and earthquake recurrence intervals are not clear, which greatly limit the accuracy of seismic risk assessment. In this study, we investigated the fault geometry and faulted landforms in Ngari area, collected OSL samples of the faulted landforms and sag ponds in Zhaxigang, Menshi and Baga towns and preliminarily discussed the ages of recent strong earthquake activity.

Study shows that the fault can be divided into three sections by Zhaxigang town and Suoduo village, and the structure and properties of each section are significantly different. In west Zhaxigang town section, the fault is dominated by dextral strike-slip with certain vertical movement, it is almost straight on the surface, with river terraces, alluvial-proluvial fans and water system faulted ranging from tens to hundreds of meters. In Zhaxigang town to Suoduo village section, the normal faulting is remarkable, the main fault constitutes the boundary fault between Ayilari Mountain and Gar Basin; fault facets and fault scarps are common along the fault line, there are also secondary faults with the same or opposite dip as the main fault developed near the piedmont basin. In east Suoduo village section, the main part of the fault is located at the south foot of Gangdise Mountain, and in addition to the piedmont fault, several approximately parallel faults are also developed on the southern alluvial-proluvial fans and moraine fans which are mainly dextrally faulted with certain vertical component.

According to the analysis of the faulted landforms and dating of the OSL samples collected from the sag ponds and faulted landforms in the west of Zhaxigang town, the east of Menshi town and the east of Baga town, the ages of recent strong earthquake activity on the fault are analyzed as follows. In the west of Zhaxigang town, the age of recent strong earthquake activity of the fault is constrained to be close to 2.34kaBP according to the average OSL dating results of KKF-3 and KKF-4. In the east of Menshi town, the recent earthquake activity age of fault f₂ is 4.67~3.01kaBP, but closer to 3.01kaBP according to the OSL dating results of KKF-11 of the youngest faulted geomorphic surface and average OSL dating results of KKF-6 and KKF-13 collected from sag ponds. In the area near Angwang village, Baga town, it is inferred that the recent strong earthquake activity age of the fault is close to 2.54kaBP according to the OSL dating results of KKF-2 collected from sag pond. If the faults of above three places are active at the same time, the age of recent strong earthquake activity of the fault is close to 2.63kaBP. The Karakorum Fault in Ngari area has obvious segment boundaries, and the activity of each segment and in its internal branch faults is most likely to be independent.

The earthquake recurrence interval on the fault is estimated to be 2.8ka according to the slip rate and the amount of displacement. From the above analysis, it can be seen the time since the last strong earthquake activity of Karakorum Fault may have been very close to the interval of earthquake recurrence. If the fault is characterized by a quasi-periodic in-situ recurrence, the energy accumulation in the fault may have reached a very high degree and the risk of recurrence of strong earthquake events of the fault may be very high, so more attention should be paid and more detailed research on the paleo-earthquake events and recurrence intervals should be carried out as quickly as possible.

With the development of photogrammetry technology and the popularity of unmanned aerial vehicles (UAVs)technology in recent years, using UAV photogrammetry technology to rapidly acquire high precision and high resolution topographic and geomorphic data on the fault zone has gradually become an important technical means. This paper first summarizes the basic principle and workflow of a new digital photogrammetry technology, SfM (Structure from Motion), which is simple, efficient and low cost. Using this technology, we conducted aerial image acquisition and data processing for a typical fault landform on the northern of Caka Basin in Qinghai. The digital elevation model (DEM)with 6.1cm/pix resolution is generated and the density of point cloud is as high as 273 points/m². The coverage area is 0.463km². Further, the terrain and slope data parallel to the fault direction are extracted by topographic analysis method, and combined with the contour map and the slope diagram generated by the DEM, a fine interpretation and quantitative study of complex multilevel geomorphic surfaces is carried out. Finally, based on the results of sophisticated interpretation of geomorphology, we got the vertical displacements of the T₁ terrace to the T₃ terrace as (1.01±0.06)m, (1.37±0.13)m and (3.10±0.11)m, and the minimum vertical displacements of the T₄ terrace and the T₅ terrace as (3.77±0.14)m and (5.46±0.26)m, respectively, through the topographic profile data extracted by DEM. Such vertical displacement parameters are difficult to obtain directly by traditional remote sensing images, which shows the great application prospect of UAV photogrammetry technology in the quantitative study of active tectonics.

Over the last two decades, in-situ cosmogenic ¹⁴C dating has become an import tool in Quaternary geology and is recognized to geoscientists because of its potential to provide information on exposure age and process rate estimates for geomorphic studies. The in-situ cosmogenic radiocarbon has a relatively short half-life(5730 yr)and is substantially more sensitive than all the other cosmogenic nuclides used so far. It is therefore particularly useful to determine surface-exposure ages of Holocene landforms and quantify erosion rates in rapidly denuding landscapes during the past few tens of thousands of years. Moreover, in situ ¹⁴C is produced in quartz which is both highly resistant to weathering and common in nature, so it can be used in combination with other in-situ cosmogenic nuclides such as ³He, ¹⁰Be,²¹Ne,²⁶Al, and ³⁶Cl to constrain complex exposure histories involving burial and/or erosion occurring over the past 25ka.
The age and slip rate of Holocene normal fault have been undoubtedly a challenge for seismologists to be faced with as result from lack of appropriate late Quaternary sediment. Recently, the cosmogenic nuclides such as ³⁶Cl of preserved, seismically exhumed normal fault scarps were used to identify the last few major earthquakes and recover their ages and displacements through the modeling of the content of ³⁶Cl in the scarp rocks.
This paper mainly summarizes the development of in-situ ¹⁴C dating, including its research history, production rate estimate, production mechanism, chemical behavior and experimental method. The potential application of in-situ ¹⁴C dating to recovering past earthquakes, their timing, and the regularity of their recurrence for preserved, seismically exhumed normal fault scarps is also introduced.

A new AMS graphite target preparation line based on Fe/H₂ reduction method has been developed in the ¹⁴C laboratory at China Earthquake Administration,China. This paper demonstrates its performance on AMS-¹⁴C of internationally-accepted standards,known-age samples and blank measurements,and also discusses the reduction conditions of the graphite. The quality of this line is tested by the measurement of background and standard samples and the results show that the blank value of this line is between 0.45 and 0.49pMC,corresponding to the limited age of 45,700a,if the machine background is subtracted. We also have tested the reproducibility and memory effect of this line. Furthermore,we carried out the dendro-dated tree ring samples test and the comparison of different labs with same samples to test the reliability. These good results allow us to use the line in routine ¹⁴C dating.

The fluvial terrace has plenty of paleoclimate and paleoenviromental information which play an important role in paleoclimate and paleoenviromental researches.In this paper,we drilled a 42.85m-long core(N06S2)in 2007,which was located in the south bank of Yangtze River at Shifuqiao in Qixia district of Nanjing City.Firstly,fine quartz grains(4～11μm)were extracted from bulk samples in dark room,and the quartz purity tests were conducted.The results show that purity can satisfy the experiment.All measurements were performed on an automated Daybreak 2200 TL/OSL system with blue(470±5nm)light stimulation and U-340 luminescence detection filters.Thick source alpha counting(TSAC)was used to measure the uranium and thorium concentrations.The potassium content was determined using flame spectrophotometer.Secondly,the preheat plateau test and dose recovery test were performed on one sample using the SAR protocol.The results indicate that the fast component dominates the OSL signals.In preheat plateau test,identical D_e in the thermal treat from 160～260℃ was observed,thus we use the preheat temperature of 220℃ for 10 seconds.The recuperation ratios of zero point are below 2％and the recycling ratios lie between 0.9 and 1.1.In dose recovery test,OSL signal sensitivity changes are well corrected.Tests of luminescence characteristics confirm the suitability of the material for OSL dating.At last,samples from this drilling core were systematically dated by optically stimulated luminescence(OSL)dating method,and samples which contain organic matters were dated by AMS¹⁴ C.The results show that the D_e values from the two methods accord with each other very well.However,OSL dating results show that there is a hiatus in this core,and the hiatus,which ranges from 1.9ka to 7.9ka,may be the result of change of Yangtze River's channel or the erosion of the river.The ages of the fluvial deposition mainly range from 0.26ka to 1.9ka and 7.9ka to 9.1ka,it could be attributed to the results of paleoclimate and sea levels change.Meanwhile,study results on pollen and spores show that the paleoclimate has changed from warm wet to temperate wet during the stage of hiatus.

This paper presents a comparison of the calendar range of individual paleoearthquake calculated by conventional calibration,Bayesian analysis of series of peat samples as well as depth-age wiggle matching.The results suggest that: (1)The Bayesian analysis provides an excellent means to enhance chronological resolution when applied to a series of radiocarbon dates from sections with clear stratigraphic relationships.Such application can assess systematic errors when combined with independent chronological information,and determine the optimum chronological information for specific events and contexts.(2)The calendar ranges of series of samples collected from the same peat but different sampling thickness were compared with that of depth-age wiggle matching.The result shows that the chronological resolution by depth-age wiggle matching for the peat sample with thickness less than 2cm could achieve less than 100a.Therefore,the condition to obtain a high resolution calendar age is to have 5～6 samples with 0.5～2cm sampling thickness each and the interval of samples is 0.5～1cm.(3)The calendar range of paleoearthquakes constrained by the Markov chain Monte Carlo(MCMC)Bayesian analysis model,which constructs the order of samples according to their position in the strata with series of radiocarbon dates,was compared with calendar range by the conventional method.The results show that Bayesian analysis could obtain high-precision calendar dates for closely spaced samples.(4)Therefore,the calendar interval of the paleoearthquake event on the middle segment of Huaiyuan Fault was inferred as 1340～1114cal a BP(2σ)by the above systematical comparsion.

Paleoseismic studies conducted along the surface rupture of the Wenchuan earthquake(M_S 8.0)of 12th May 2008 provide important information regarding earthquake reoccurrence intervals and slip rates of the Longmen Shan Fault zone.The Leigu trench was excavated along the middle segment of the surface rupture of the Yingxiu-Beichuan Fault zone.Based on the syntectonic sedimentary structure,two earthquake events,including the Wenchuan event,were identified at this site.This study utilizes Optically Stimulated Luminescence(OSL)dating of samples collected from the Leigu trench section,using SMAR(Sensitivity-corrected Multiple Aliquot Regenerative-dose)protocols.AMS¹⁴C dating was also carried out on charcoal from the same sediments.OSL ages are generally consistent with the calibrated AMS¹⁴C ages(cal a BP)for the same units.The penultimate earthquake event similar to Wenchuan earthquake scale in this region occurred(2.1?0.2)ka to(1.1?0.2)ka.

Primary evidence of the latest tectonic deformation style and the activity age of the Dayi Fault in the Sichuan Basin are obtained by field geological mapping,and surveying with the help of 3D scanner and total station.In the region of Wenshangou-Longfengchang,northeast of Dayi county on the northwestern wall of the fault,the time of Cretaceous and Neogene strata's gentle folding was measured to be between late Neogene and early Pleistocene.And obviously its forming time is later than the Longmen Shan Fault which controls the northwest boundary of Sichuan Basin's Mesozoic strata and shows a thrust-nappe structure.With the help of oil prospecting data,fault plane inclines to northwest,dip angle changes from 10°～20° in the deep to 70° at near-surface,and depth of the upper faulted point is about 200～300m.Geological and geomorphologic evidence shows that Holocene is its latest active time.The latest tectonic deformation on the Dayi Fault is represented by Holocene fold.Topographically,the deformation appears as continuous piedmont hillocks with traceable length of 2.5km,distributed en echelon in the piedmont of the Longmen Mountains and with the plane shape of single hillock being ellipse.Accordingly the Dayi Fault is inferred as a Holocene active blind fault on the basis of hillocks' section shape.

On 12 May 2008,a magnitude 8.0 earthquake occurred beneath the steep eastern margin of Tibetan plateau in Sichuan,China.Rupture occurred over a length of～240km along the central Longmenshan Fault(Beichuan-Yinxiu Fault)and ～72km along the Longmenshan piedmont fault(Guanxian-Jiangyou Fault).In order to know clearly the activity of the middle segment of Longmenshan Fault,we surveyed the earthquake rupture and excavated 5 trenches in the north part of the central Longmenshan Fault.Four of the five trenches have revealed the deformation of the Wenchuan earthquake and the characteristics of strong earthquake activity on this segment.The 4 trenches are briefly described as follows.The Fenghuang village trench locates on T₂ terrace or T₃ terrace of Pingtong River.The trench logs show that there is another earthquake event except the Wenchuan earthquake.As a tectonic deformation character,the thrust fault is exposed on the surface,the underground soils were thrust over the cultivated surface soil,forming thrust nappe and extrusion wedge.The bedrock near the fault has been compressed and fractured seriously,which is represented by overlap of some old scarps with new ones on the ground surface.The trench on T₁ terrace at Pingtong Panxuanlu records the zigzag deflections of marker bed.According to the recovery of marker bed,it is possible that there was an earlier earthquake event whose magnitude is equivalent to the present Wenchuan earthquake,because the footwall is higher than the hanging wall after the marker bed flattened,and the Wenchuan earthquake scarp on flood plain and T1 terrace is much lower than the scarp at the trench site.The scarp with a length of～20m and height of～2.7m is revealed by the trench excavated near the Da′ai School,but we can't see obvious signs of fault and faulting.Perhaps the fault displacement is represented by slightly folding of each deposit layer,which is one of the surface deformation models of thrust faulting.On T₁ terrace at Miaoziwan village,Nanba town,the trench displays that the vertical displacement of arc-deflection on marker bed is equal to the earthquake scarp height,indicating that this phenomenon is caused by the present earthquake event alone.Now,there are no results of dating samples,so we obtained the topographical age by comparing the adjacent surfaces.According to the dating results of terrace,the forming time of T₁ terrace is about 3000～5000a and T₂ terrace about 12000～20000a.It is revealed that the recurrence interval of strong earthquake on the northern segment of central Longmenshan Fault is more than 3000a.

In the historical rocords,there have been no comparable earthquakes with the May 12 Wenchuan earthquake in Chengdu and Longmenshan mountain region.Then,whether the ancient earthquake traces with comparable magnitude in the geological records can be found has become an important scientific issue.The authors and other members of Wenchuan earthquake geological investigation team did fieldwork in the earthquake region for more than one month.Four trenches and one geologic section were excavated along the middle segment of surface faulting of both the central fault and the mountain front fault.And geomorphologic surfaces of deformation were measured.In this paper,we discuss the fact that there is prehistory large earthquake along the seismogenic fault of Wenchuan earthquake from analyzing the accumulated deformation of old and young fault scarps or geomorphologic surfaces,trenching,and comparing the activities of related faults and so on.The result shows that whether at Xiaoyudong,Leigu located on the central fault or Bailu,Hanwang on the mountain front fault,or at other places along the surface faulting of the the Wenchuan earthquake,the height of the fault scarp on the second terrace has a multiple relation with that on the first terrace after the Wenchuan earthquake.The 4 trenches reveal that the dislocation of the marker strata of the second terrace on both sides of fault is twice of that of the Wenchuan earthquake,which shows that there was an earthquake event with the same scale of surface deformation of this M_S8.0 Wenchuan earthquake between the formation time of the second terrace in Lomhmenshan area and the May 12 Wenhucan earthquake.

The fine-grain quartz extracted from two burnt reworked loess samples LEDL0588H and LEDL0365 was measured by modified SAR and SMAR protocols for OSL dating.The fast component is dominant in OSL signals.The identical De in the thermal treatment from 180～260℃was showed in preheat plateau test using both protocols.As was shown in measuring the values T_X/T_N and L_N/L_N as a function of preheat temperatures,in dose recovery test in SAR and the value of L_N/L_N in SAR and SMAR protocols,OSL signal sensitivity changes were well corrected.Both methods can be used to estimate De of the two samples properly for OSL dating.Although located at different strata levels,the similar OSL ages of two samples suggest the latest time they were burnt may be at a same period of human activity.

Based on 44 ¹⁴C dates of humic acids and humins under different weather conditions,a statistics analysis was made to estimate their performance in paleosols.The following suggestions are reached:(1)A normal distribution analysis for HA/HM values deduced from 44 ¹⁴C dates results in average value of 0.98 with standard deviation of 0.20.This seems that the humin may be the oldest fraction of soil and its ¹⁴C age can represent the age of the paleosol.(2)The relationship between HA/HM value and the age of paleosol samples shows that the ages of humic acid and humin are indistinguishable for samples deposited in late Quaternary,but are obviously different from paleosol samples in Holocene.Their different behaviors in late Quaternary and Holocene may be related to the pollutant due to Holocene soil exposed to the surface and easily influenced by pollutant.Therefore it is suggested to use the different fractions for Holocene soil to obtain reliable radiocarbon ages for soil samples.(3)Assuming that the modern carbon pollutant entered into soil one-off,the amount of modern carbon into original carbon is estimated to be about 1.49% for late Quaternary soil sample,but this value increases to 21.37% in Holocene soil.Therefore,the amount of pollutant for Holocene soil is over 15 times than that for late Quaternary soil.If such pollutant continues to enter into soil with similar quantity during deposition,the impact percentages are 5.71% and 30.46% for late Quaternary and Holocene soil samples,respectively.The amount of modern carbon by continuously entering into soil is 2.6 times that of the one-off entering into soil for one sample in the same condition.It is further needed to state that which fractions could obtain more reliable ages for soil samples still depends on other factors such as geomorphic location,climatic zone,and soil type.

This paper introduces a simple and practical way to construct quenching calibration curve for tritium DPM measurements basing on efficiencies of a series of known activity standard sources and quenching parameter SQP(E)used to define the quench level in Quantulus 1220.Ten standard sources and two test samples were prepared with tritium-free water as quenching materials and progressively added to Hisafe 3 cocktail.A linear curve or polynomial function curve was fitted with each pair of quench parameter SQP(E)and efficiency of standard source.The test sample demonstrated that the error of linear curve was small within routine quenching range of 776 to 785.Therefore,the quenching calibration curve can be beneficial to improving accuracy and reliability of tritium counting.

This paper presents the importance of converting the radiocarbon date into calendar year in paleoearthquake study and summarizes the history of the calibration curve as well as the current progress back to 50ka BP. The calibration method and computer program were also mentioned.

We use the Chinese Sucrose Standard and synthetical benzene as well as 13 paired-samples to assess the performance of a new Quantulua-1220 bought in July,2004. The results show that:1) when the background is below 0.5cpm and the fluctuation does not exceed 4‰ in the measuring surrounding,we infer the maximum datable age for this instrument would be up to almost 48ka; 2) The quench SQP(E) parameters of 261 radiocarbon samples vary from 700 to 758. The median is 735.522 and standard deviation is 9.150 57. The maximum age error caused by quenching factor is below 80a; 3) The t test results of 13 paired-samples indicate that the new Quantulua-1220 became stable after it ran for 10 months and the ages are indistinguishable in statistical test from ages supplied by other similar LSCs.

A trench across the Haiyuan active fault zone reveals many layers of charcoal with human bone,scruff,ceramic pieces or hearth ruin as well as three colluvial wedges in Ciergou paleoearhquake profile which is located on the northern margin of Tibet Plateau. It is important to distinguish these historical remnants as whether or not they are the product of earthquake. 12 radiocarbon dates and 6 post-IR OSL dates were determined from charcoal samples corresponding to human activity and sediments or burned clay samples around charcoal samples respectively. The ages of charcoal which mainly range from 1000 to 2400a BP were sharply younger than the age of strata. The age of living site inferred from charcoal with scruff,ceramic pieces,does not agree with timetable of the historical strong earthquake record. This evidence could indicate that the living site ruins is not the product of historical earthquake. The penultimate paleoearthquake prior to 1920 AD earthquake occurred in 21.8～14.5ka which was constrained by post-IR OSL dates. These dates would help to better understand the strong earthquake recurrence interval of the Haiyuan active fault zone.

The largest eruption of the Tianchi Volcano in historical period had not been recorded in historical document. Therefore,the determination of the accurate date of this largest eruption event is of great importance to the estimation of the eruption interval,the evaluation of the eruption risk and the hazard prediction of the future eruption. Basing on the systematical ¹⁴C dating of a well-preserved large carbonized wood,Liu Ruo-xin et al (1997) concluded that the largest historical eruption of the Tianchi Volcano occurred in 1215?15 AD. However,this conclusion has evoked much controversy. Horn et al (2000) suggested that the eruption time of Tianchi Volcano should be in 969?20 AD as determined from the age of a slab of carbonized wood collected from the North Korean side in a pumice fallout deposit. Earlier,Dunlap (1996) reported a wiggle-matched age of 1039?18 AD determined at the University of Arizona. Moreover,some experts favor 870?170 AD,which was the average of 53 radiocarbon ages of carbonized wood collected from the ignimbrite. In this paper,the eruption time of the Tianchi Volcano has been studied through detailed field investigation and careful selection of representative profile for collecting radiocarbon samples. The radiocarbon dates of 16 samples of carbonized wood including a piece of bark collected from ignimbrite around the Tianchi Volcano show that it is reasonable to consider the age of 1215?15 as the eruption time of the Tianchi Volcano. All of the radiocarbon ages of the carbonized wood are older than the true age of volcanic eruption,the largest deviation from which is 800yr,but the age of the bark is close to that of the Tianchi Volcano eruption. This may imply that the age of bark sample may provide better constraint on the date of volcanic eruption. The radiocarbon ages of black ignimbrites from Heishihe River,Pumice Forest,and Jinjiang Gorge show that they are also the product of 1215?15 AD eruption.

More than ten volcanoes of Jingpohu Holocene Volcanic Group consist of five small eruption centers situated at southwest area and northeast area separately. Southwest area includes four eruption centers, namely “Crater Forest”, “Daganpao”, “Wudaogou” and “Mihunzhen”, respectively. Northeast area has only one eruption center called “Hamatang”. Eruptive materials include mainly lava flow, splash deposit and airfall deposit. Volcanic cone consists of cinder, bomb, driblet and thin lava flow. The thickness of a

Recent magnetostratigraphic and lithostratigraphic studies in the western Tarim basin have led to better constrained depositional and deformational histories. As a lithostratigraphic unit, the Xiyu Formation consists an abruptly upward-coarsening fanglomerate locally interbedded with lenticular sandstone and sandy mudstone beds. It is unconformably or disconformably overlain by the Wusu formation. The concordantly underlying Atushi Formation is predominately fluvial siltstones, sandy mudstones, and rippled

A comprehensive study of chronology for the lower terraces along several major rivers in the Yanhuai basin and its adjacent areas is made by TL,IRSL and 14C dating as well as the Spore-pollen analysis method. The deposited ages of sediments heve been dated and the formation times of the geomorphic surfases for these lower terraces are estimated. The results show that the lower terraces in this region are associated with the regional motion and the climate conditions since late Pleistocene time