Step-over of strike-slip faults and overpressure fluid favor occurrence of foreshocks:Insights from the 1975 Haicheng fore-main-aftershock sequence,China

This study analyzed and summarized in detail the spatial and temporal distributions of earthquakes,tidal responses,focal mechanisms,and stress field characteristics for the M 7.3 Haicheng earthquake sequence in February 1975.The foreshocks are related to the main fault and the conjugate faults surrounding the extension step-over in the middle.The initiation timing of the foreshock clusters and the original time of the mainshock were clearly modulated by the Earth's tidal force and coincided with the peak of dilational volumetric tidal strain.As a plausible and testable hypothesis,we proposed a fluid-driven foreshock model,by which all observed seismicity features can be more reasonably interpreted with respect to the results of existing models.Together with some other known examples,the widely existing step-over along strike-slip faults and associated conjugate faults,especially for extensional ones in the presence of deep fluids,favor the occurrence of short-term foreshocks.Although clustered seismicity with characteristics similar to those of the studied case is not a sufficient and necessary condition for large earthquakes to occur under similar tectonic conditions,it undoubtedly has a warning significance for the criticality of the main fault.Subsequent testing would require quantification of true/false positives/negatives.

Zircon U–Pb geochronology and Hf isotope geochemistry of magmatic and metamorphic rocks from the Hida Belt, southwest Japan

Zircon U–Pb and Hf isotope data integrated in this study for magmatic and metamorphic rocks fromthe Hida Belt,southwest Japan,lead to a new understanding of the evolution of the Cordilleran arc system along the ancestral margins of present-day Northeast Asia.Ion microprobe data for magmatic zircon domains from eight mafic tointermediate orthogneisses in the Tateyama and Tsunogawa areas yielded weighted mean 206Pb/238U ages spanning the entire Permian period(302–254 Ma).Under cathodoluminescence,primary magmatic growth zones in the zircon crystals were observed to be partially or completely replaced by inward-penetrating,irregularly curved featureless or weakly zoned secondary domains that mostly yielded U–Pb ages of 250–240 Ma and relatively high Th/U ratios(>0.2).These secondary domains are considered to have been formed by solid-state recrystallization during thermal overprints associated with intrusions of Hida granitoids.Available whole-rock geochemical and Sr–Nd isotope data as well as zircon age spectra corroborate that the Hida Belt comprises the Paleozoic–Mesozoic Cordilleran arc system built upon the margin of the North China Craton,together with the YeongnamMassif in southern Korea.The arcmagmatismalong this systemwas commenced in the Carboniferous and culminated in the Permian–Triassic transition period.Highly positiveεHf(t)values(>+12)of late Carboniferous to early Permian detrital zircons in the Hida paragneisses indicate that there was significant input from the depleted asthenospheric mantle and/or its crustal derivatives in the early stage of arc magmatism.On the other hand,near-chondriticεHf(t)values(+5 to−2)of magmatic zircons from late Permian Hida orthogneisses suggest a lithospheric mantle origin.Hf isotopic differences between magmatic zircon cores and the secondary rims observed in some orthogneiss samples clearly indicate that the zircons were chemically open to fluids or melts during thermal overprints.Resumed highly positive zirconεHf(t)values(>+9)shared by Early Jurassic granitoids in the Hida Belt and Yeongnam Massif may reflect reworking of the Paleozoic arc crust.

A combination of tides and nontidal variations in ocean bottom pressure may generate interannual slip fluctuations in the transition zone along a subduction plate interface

The tidal triggering of earthquakes has been studied for many years.The discovery of slow earthquakes in the early 2000s,including slow slip,has urged scientists to investigate the tidal responses of these earthquakes due to their sensitivity to weak stress perturbations.Previous studies have shown that slow earthquakes correlate with diurnal and semidiurnal tides and seasonal variations in surface loads more clearly than ordinary earthquakes.However,little is known about long-term responses to external stresses.In this paper,based on a widely accepted frictional law for faults,a mechanism is proposed by which nontidal variations in ocean bottom pressure,when combined with tides,pro mote the occurrence of slow earthquakes.Because slow earthquakes accompany a slip on the plate interface,this mechanism allows one to estimate slip modulations.A one-degree-of-freedom slip model is constructed and applied to Ise Bay in the Tonankai region of southwestern Japan,where large-scale ocean mass redistributions have occurred.The model calculated with parameters determined from the observation of tectonic tremors is quantitatively consistent with the slip during 1997-2013 inferred from GNSS data,suggesting that the decrease in the sea-level change in approximately 2006 could cause the accele ration of a slip observed after that.This result implies that the decreases in sea level in approximately 1996 and 2014 could also cause subsequent slip accelerations.These three slip acceleration periods temporally coincide with the increases in background seismicity in a shallower portion of the plate interface.These changes in seismicity are common to shallow earthquakes in the Tokai area,and a similar model can reproduce them.Further studies are expected to reveal causality between shallow earthquakes and long-term slip fluctuations based on modeling that considers changes in the frictional property along the plate interface.

Sedimentary Evolution of the Holocene Subaqueous Clinoform off the Southern Shandong Peninsula in the Western South Yellow Sea

Based on the stratigraphic sequence formed since the last glaciation and revealed by 3000 km long high-resolution shallow seismic profiles and the core QDZ03 acquired recently off the southern Shandong Peninsula, we addressed the sedimentary characteristics of a Holocene subaqueous clinoform in this paper. Integrated analyses were made on the core QDZ03, including sedimentary facies, sediment grain sizes, clay minerals, geochemistry, micro paleontology, and AMS 14 C dating. The result indicates that there exists a Holocene subaqueous clinoform, whose bottom boundary generally lies at 15–40 m below the present sea level with its depth contours roughly parallel to the coast and getting deeper seawards. The maximum thickness of the clinoform is up to 22.5 m on the coast side, and the thickness contours generally spread in a banded way along the coastline and becomes thinner towards the sea. At the mouths of some bays along the coast, the clinoform stretches in the shape of a fan and its thickness is evidently larger than that of the surrounding sediments. This clinoform came into being in the early Holocene(about 11.2 cal kyr BP) and can be divided into the lower and upper depositional units(DU 2 and DU 1, respectively). The unit DU 2, being usually less than 3 m in thickness and formed under a low sedimentation rate, is located between the bottom boundary and the Holocene maximum flooding surface(MFS), and represents the sediment of a post-glacial transgressive systems tract; whereas the unit DU 1, the main body of the clinoform, sits on the MFS, belonging to the sediment of a highstand systems tract from middle Holocene(about 7–6 cal kyr BP) to the present. The provenance of the clinoform differs from that of the typical sediments of the Yellow River and can be considered as the results of the joint contribution from both the Yellow River and the proximal coastal sediments of the Shandong Peninsula, as evidenced by the sediment geochemistry of the core. As is controlled mainly by coactions of multiple factors such as the Holocene sea-level changes, sediment supplies and coastal dynamic conditions, the development of the clinoform is genetically related with the synchronous clinoform or subaqueous deltas around the northeastern Shandong Peninsula and in the northern South Yellow Sea in the spatial distribution and sediment provenance, as previously reported, with all of them being formed from the initial stage of the Holocene up to the present.

A laboratory acoustic emission experiment and numerical simulation of rock fracture driven by a high-pressure fluid source

In order to improve our understanding of rock fracture and fault instability driven by high-pressure fluid sources, the authors carried out rock fracture tests using granite under a confining pressure of 80 MPa with fluid injection in the laboratory. Furthermore, we tested a number of numerical models using the FLAC;modeling software to find the best model to represent the experimental results. The high-speed multichannel acoustic emission（AE） waveform recording system used in this study made it possible to examine the total fracture process through detailed monitoring of AE hypocenters and seismic velocity.The experimental results show that injecting high-pressure oil into the rock sample can induce AE activity at very low stress levels and can dramatically reduce the strength of the rock. The results of the numerical simulations show that major experimental results, including the strength, the temporal and spatial patterns of the AE events, and the role of the fluid can be represented fairly well by a model involving（1） randomly distributed defect elements to model pre-existing cracks,（2） random modification of rock properties to represent inhomogeneity introduced by different mineral grains, and（3）macroscopic inhomogeneity. Our study, which incorporates laboratory experiments and numerical simulations, indicates that such an approach is helpful in finding a better model not only for simulating experimental results but also for upscaling purposes.

Geochemical and Grain-Sized Implications for Provenance Variations of the Central Yellow Sea Muddy Area Since the Middle Holocene

Based on high-resolution analysis to a 280-cm long sediment core obtained from the muddy area in the central Yellow Sea, we examined the provenance of muddy sediments and discussed the changing marine sedimentary environment since the middle Holocene. The results indicated that fine-grained sediments in the muddy area were mainly derived from the Huanghe(Yellow River) and Changjiang(Yangtze River) with considerable stepwise variations during the past 6.6 kyr. The Yellow Sea Warm Current was initiated at 6 kyr when the sea level was high together with the enhanced East Asian Winter Monsoon. These in combination established the framework of shelf circulation in the Yellow Sea that began to trap the river-derived fine-grained sediments. From 4.9 kyr to 2.8 kyr, both the Kushiro Current and East Asian Monsoon were significantly weakened, reducing the delivery of Changjiang sediments to the muddy area. As a result, the sediments were mainly originated from the Huanghe. From 2.8 kyr to 1.5 kyr the continuously weakened East Asian Winter Monsoon and enhanced Yellow Sea Warm Current entrapped more fine-grain sediments. Whereas the enhanced East Asian Winter Monsoon and the human caused increase in sediment load of the Huanghe since 1.5 kyr, and direct delivery of Huanghe sediments to the Yellow Sea during 1128–1855 AD might dominated the sedimentation in the study area. The stepwise variations of the sediment provenance and composition of the Central Yellow Sea muddy sediments are of importance to understanding the formation of muddy deposit in the central Yellow Sea and the associated variations of marine environment since the middle Holocene.

Liquid Immiscibility of Boninite in Xiangcheng, Southwestern China, and Its implication to Genetic Relationship between Boninite and Komatiitic Basalt

Boninitic rocks and associated high-magnesian basalt and high-iron tholeiite in the Xiangcheng area constitute the basal horizon of the arc volcanic sequence in the Triassic Yidun Island-Arc, southwestern China. The boninite occurs as pillow, massive and ocellar lavas; the last one possesses well-developed globular structure and alternates with the former two. The boninite is characterized by the absence of phenocrysts of olivine and low-Ca pyroxenes and by low CaO/Al2O3 ratios (<0.67) and high Cr (>1000 ppm) and Ni (>250 ppm). The normalized abundance patterns (NAP) of trace elements to primitive mantle are similar to the NAP of low-Ca modern boninites and SHMB in the Archaean and Proterozoic.

Rock magnetic property of gravity core CSH1 from the northern Okinawa Trough and the effect of early diagenesis

Detailed rock magnetic investigations were undertaken at 2 -4 cm interval for the gravity core CSHI （with a length of 17.36 m） from the northern Okinawa Trough. Time-scale of the core was constructed by two characteristic tephras and foraminferal assemblages, indicating an age of 50 ka for the bottom of the core. Except for three tephras and abrupt decrease in surface, there are little changes in all kinds of rock magnetic parameters that can be correlated to the climate change for the last 50 ka. Different from the common sediments, most S-ratios （S equals the negative ratio of IRM-0.3T to SIRM, which is an indicator of low coercivity content） of the sediments are smaller than 0. 9, which implies a substantial amount of magnetic minerals with high coercivity. The existence of iron sulphide （ greigite or pyrrhotite） is revealed by representative susceptibility - temperature curves showing 200 350 ℃ Curie temperature in addition to 580 ℃ of magnetite, and also by awful smell during heating and dark heating products. Both the occurrence of authigenic iron sulphide and quick decrease of magnetic parameters near the surface clearly show that sediments from Core CSHI have undergone early diagenesis. The featureless magnetic changes of the whole core except for three tephras mean that the post-depositonal alteration is so strong that most original signals have been destroyed. For the same reason, the organic matter in sediment and sulphate in pore water must have been consumed along with dissolution, precipitation of iron and manganese happening sequencially during the redox reaction series. Great caution must be taken when using these altered chemical parameters for the interpretation of climatic changes.

Amelioration of acidic soil using fy Ash for Mine Revegetation in PostMining Land

This paper described the use of fy ash for soil amelioration of acidic soils to promote plant growth.In mining sites,acid sulfate soils/rocks,which contain sulfde minerals(e.g.pyrite FeS_(2)),have appeared as a result of overburden excavation.The excessively acidic condition inhibits plant growth due to the dissolution of harmful elements,such as Al,Fe,and Mn.Fly ash,an alkaline byproduct of coal combustion generated in thermal power plants is expected to be adopted to ameliorate acidic soils.However,the mixing ratio of fy ash must be considered because excessive addition of fy ash can have a negative impact on plant growth due to its physical/chemical properties.The pot trials using Acacia mangium demonstrate the evolution of plant growth with a 5%–10%addition of fy ash into acidic soil.When the acidic soil has a high potential for metal dissolution,the metal ions leached from the acidic soil are large,making it difcult to improve plant growth due to osmotic and ionic stress.This work suggests that the efects of fy ash on metal ions leached from the soil have to be considered for the amelioration of acidic soil.

Stick–slip behavior of Indian gabbro as studied using a NIED large-scale biaxial friction apparatus

This paper reports stick-slip behaviors of Indian gabbro as studied using a new large-scale biaxial friction apparatus, built in the National Research Institute for Earth Science and Disaster Prevention （NIED）, Tsukuba, Japan. The apparatus consists of the existing shaking table as the shear-loading device up to 3,600 kN, the main frame for holding two large rectangular prismatic specimens with a sliding area of 0.75 m^2 and for applying normal stresses an up to 1.33 MPa, and a reaction force unit holding the stationary specimen to the ground. The shaking table can produce loading rates v up to 1.0 m/s, accelerations up to 9.4 m/s^2, and displacements d up to 0.44 m, using four servocontrolled actuators. We report results from eight preliminary experiments conducted with room humidity on the same gabbro specimens at v = 0.1-100 mm/s and an = 0.66-1.33 MPa, and with d of about 0.39 m. The peak and steady-state friction coefficients were about 0.8 and 0.6, respectively, consistent with the Byerlee friction. The axial force drop or shear stress drop during an abrupt slip is linearly proportional to the amount of displacement, and the slope of this rela- tionship determines the stiffness of the apparatus as 1.15 × 10^8 N/m or 153 MPa/m for the specimens we used. This low stiffness makes fault motion very unstable and the overshooting of shear stress to a negative value was recognized in some violent stick-slip events. An abrupt slip occurred in a constant rise time of 16-18 ms despite wide variation of the stress drop, and an average velocity during an abrupt slip is linearly proportional to the stress drop. The use of a large-scale shaking table has a great potential in increasing the slip rate and total displacement in biaxial friction experiments with large specimens.

Is clustered seismicity an indicator of regional stress?Insights from earthquake sequences in Yongning-Luguhu faulted basin,Southwest China

Using hypocenter relocation,moment tensor inversion,stress field inversion,and fault slip tendency analysis,this study systematically investigated three M5.5-5.8 earthquake sequences that occurred after 2000 in the Yongning-Luguhu faulted basin in the middle of the Lijiang-Xiaojinhe fault zone within the Sichuan-Yunnan block,Southwest China.Our results show that since the 2008 Wenchuan earthquake,the tectonic stress pattern in this area may have changed and that b-values estimated for the earthquake sequences show evidence of an increasing trend in stress in the study area.Seismicity in the small-scale faulted basin adjacent to the large-scale fault zone is a possible indicator of regional stress.We also note that the aftershocks of the M5.7 earthquake sequence in 2012 and the M5.5 earthquake sequence in 2022 show relatively clear fluid diffusion-triggering characteristics.Overpressure of deep fluids is still the main factor driving seismic activity in the region,and we propose that the background tectonic stresses have not yet reached critical levels.

Focal Mechanism Solution of the February 23,2014,M_L3.8 Rongchang Earthquake with the CAP(Cut and Paste)Method

A M_L3.8 earthquake occurred on February 23,2014 in Rongchang County,which is located at the southern edge of the Sichuan Basin in the border area between Sichuan and Chongqing. This paper presents results of focal mechanism solution of this earthquake using the CAP( cut and paste) method based on broadband seismograms recorded by regional seismic stations. Our results show that the moment magnitude is M_W3. 09 and focal depth is 3km. The hypocenter of this earthquake is located close to a buried fault in the Luoguangshan anticline. Oil prospecting and deep drilling data indicate that this buried fault is a thrust fault,striking SW230°,dipping NW45°,and 1. 7km deep. There are some injection wells within the anticline,and significant injection-induced earthquakes were observed during the periods of injection of waste water into the deep formations through those wells. The best double couple solution of the M_L3.8 earthquake is 247°,48°and 104° for strike,dip and rate,respectively,for one nodal plane( and 46°,44° and 74°for another nodal plane),which is in agreement with the geometry of the buried fault.Therefore,we conclude that the M_L3.8 Rongchang earthquake is possibly the result of faulting along the buried reverse fault induced by water injection under the compressive stress regime in the area.

Uneven Distribution of Pseudotormentus De Wever et Caridroit(Radiolaria,Protozoa):Provincialism of a Permian Planktonic Microorganism

The Permian planktonic distribution is not well known,in contrast to other fossil distributions of nekton and benthos.Radiolaria are representative microfossils of plankton in the Permian palaeocean.This study compares both correlated radiolarian occurrences（Pseudotormentus De Wever et Caridroit and Quadriremis Nazarov et Ormiston） in literature data from the Pacific Rim and quantitative data from the Liuhuang and Gujingling sections in South China.Pseudotormentus distributions are concentrated in the Panthalassa,whereas Quadriremis occurrences are distributed over both the Panthalassa and the Palaeotethys.The uneven distribution of Pseudotormentus seems to have been controlled by a difference in the oceanic basins,indicating the presence of faunal differences in Permian planktonic microorganisms between the Panthalassa and the Palaeotethys.In other words,this study infers the provincialism of Permian planktonic microorganisms.The uneven distribution is explainable by a hypothesis that Pseudotormentus was strongly affected by a Panthalassan equatorial current.

Integrated Radiolarian and Conodont Biostratigraphy of the Middle to Late Permian Linghao Formation in Northwestern Guangxi, South China

The Permian radiolarian zones and their correlations with conodont zones or other chronostratigraphic schemes are still under debate. In this study, four genera, 21 species and two subspecies of radiolarians together with one genus and six species of conodonts were recovered from the Linghao Formation cropping out at the Longwangpo(LWP) section, northwestern Guangxi, South China. Six radiolarian interval zones and one abundance zone are recognized in the section, namely in ascending order, the Follicucullus scholasticus, Albaillella cavitata, A. protolevis, A. levis, A. excelsa, A. triangularis Interval zones and A. yaoi Abundance Zone. They are correlated with the Clarkina dukouensis, C. guangyuanensis and C. orientalis conodont zones recognized at the same section. Based on our data, the F. scholasticus Interval Zone and the lowermost part of A. cavitata Interval Zone are recognized to be upper Capitanian age, whereas the four Albaillella Interval zones are of Lopingian age(Wuchiapingian to the late Changhsingian). Two previously known Changhsingian radiolarian zones, namely the A. triangularis and A. yaoi Interval zones, should be extended down to the uppermost Wuchiapingian in this studied section.

Effect of Rock Structure on Statistical Characteristics of Acoustic Emission

A comparative study on acoustic emission during deformation of two kinds of granites with different structures under triaxial compression was performed using a new acoustic emission recording system with full-waveform record and broad-dynamic range. One is the Inada aplite-granite of homogeneous structure from Japan and the other is the Mayet granite with cemented natural joints from France. For the former granite, acoustic emission events are dispersed randomly and there is no clear clustering along the major fracture. For the latter granite, acoustic emission events are mainly concentrated near the joints. Acoustic emission events occur synchronously with the volumetric dilatation in the former one but far earlier than the volumetric dilatation in the latter one. The two kinds of granites are also clearly different in the frequency spectrum of acoustic emission. The former has a narrower frequency band and a higher frequency component, whereas the latter has a wider frequency band and generally a

Measurement of Volcanic SO₂Concentration in Miyakejima Using Differential Optical Absorption Spectroscopy (DOAS)

Since the volcanic eruption in 2000, continuous monitoring of sulfur dioxide (SO2) gas has been conducted with in-situ samplers located along the seashore road in Miyakejima, a volcano island around 180 kmsouth of Tokyo. The purpose of these sampling measurements has been to issue warning on the hazardous air pollution to the local residents. Therefore, the resulting data do not provide direct information on pollution levels inside the restricted areas where high concentration of SO2 still takes place frequently. From the ecological point of view, it is desirable to have pollution data covering wider regions of the island. In this paper we report on our differential optical absorption spectroscopy (DOAS) measurements carried out inside the highly-polluted, restricted areas in Miyakejima in December 2009 and September 2010. The system is based on continuous light emitted from a xenon light sources, while detector setups consisting of a telescope and a compact spectrometer detect the light after passing a nearly horizontal optical path of460 m-1300 m. By virtue of the portability of the DOAS observation systems, we achieved the measurement of the concentrations inside the restricted districts in the eastern and southwestern parts of the island. The DOAS results in both of these districts revealed the occurrence of pollution of volcanic gas even when no pollution was observed at nearby sampling stations. In addition, simultaneous measurements with two nearly orthogonal DOAS paths were conducted for examining the spatial distribution of the volcanic gas over the spatial range of several hundred meters. The result of this two paths measurement has indicated the importance of orography, in addition to the wind speed and wind direction, in determining the spatial concentration of SO2 emitted from the volcano crater.

Fine Velocity Structure and Relocation of the 2010 M_L 5.1 Earthquake Sequence in the Rongchang Gas Field

Based on data collected from a temporal seismic network, and in addition to the data from some nearby permanent stations, we investigate the velocity structure and seismicity in the Rongchang gas field, where significant injection-induced seismicity has been identified. First, we use receiver functions from distant earthquakes to invert detailed 1-D velocity structures beneath typical stations. Then, we use the double-difference hypocenter location method to re-locate earthquakes of the 2010 MLS. 1 earthquake sequence that occurred in the region. The re-located hypocenters show that the 2010 MLS. 1 earthquake sequence was distributed in a small area surrounding major injection wells and clustered mostly along pre-existing faults. Major earthquakes show a focal depth less than 5km with a dominant depth of -2km, a depth of major reservoirs and injection wells. We thus conclude that the 2010 ML 5. 1 earthquake sequence might have been induced by the deep well injection of unwanted water at a depth - 3km in the Rongchang gas field.

济州岛西南泥质区粒度组分变化的古环境应用

利用激光粒度仪对位于东海陆架济州岛西南泥质区的B2孔进行了沉积物粒度分析,根据标准偏差变化检出了B2孔含有4个粒度组分:＞65.6、65.6～10.5、10.5～1.3和＜1.3 μm,其中＞65.6μm粗组分含量很低,主要是以底栖有孔虫为主的生源沉积.各组分平均粒径和粒度含量随孔深的变化显示了65.6～10.5μm组分在B2孔含量较高(21%～30%),变化最明显,是该孔对环境变化最敏感的粒度组分.研究表明该敏感组分的粒度含量和平均粒径变化主要受东亚冬季风的强弱变化制约,其变化恢复的近2 ka来东亚冬季风变化和中国东部气候变化序列具有很好的一致性,证明65.6～10.5 μm粒度组分可以作为东亚冬季风的替代指标.

南黄海中部泥质区YE-2孔8.4kaBP来的沉积特征

对取自南黄海中部泥质区YE-2钻孔的6.1m岩心进行了年代学、沉积学、微体古生物学和U3K7′海表温度分析,结果显示,该孔沉积物基本类型为黏土质粉砂,8400aBP来的沉积环境可分为3段:8.4～6.9kaBP为砂含量达13%的滨岸浅水环境;6.9～6.1kaBP为砂含量8%的滨岸浅水向稳定浅海过渡的环境;6.1～0kaBP为基本不含砂的黏土质粉砂稳定浅海环境。表层海水温度(SST)在滨岸浅水阶段较低,平均约14.2℃;在第2阶段从6.9kaBP开始增加,最高达18.1℃,指示了黄海暖流的入侵;6.4kaBP增温结束后,浅海阶段SST稳定在15～16℃之间,同时有3个SST平均为13.9℃的短暂低温期,大致为5.7～5.2、3.7～3.2和2.3～1.8kaBP。在稳定浅海环境的黏土质粉砂地层中发现了罕见的3个砂质粉砂质粗粒级夹层,大致形成于6.0、3.9和2.5kaBP,其粒度具有风暴沉积特征,重矿物表现出变质岩特点,U3K7′-SST和黏土矿物指示其沉积环境的温度偏高。上述特征与岩心其他所有层位差异较大,显示了异地搬运的特征,可能为风暴沉积。根据AMS14C测年,不考虑风暴沉积,YE-2岩心的沉积速率在50.7～75.6cm/ka之间。