第三的英文译语怎么说-特朗普取消访问丹麦
2023年3月30日发(作者:牛津一年级英语)
Earthquake Research in China
Volume 24,Number J,2010
Ding Rui,Ren Junjie,and Zhang Shimin
Institute of Crustal Dynamics,China Earthquake Administration,Beijing 100085,China
The northern piedmont fault of Wutai Mountain is located at the north of the Shanxi
Graben system,which is the dominating fault of the south boundary of the Fanshi-Daixian
depression.This paper discusses the fault activity and paleoearthquakes around the
Nanyukou segment of the northern piedmont fault of Wutai Mountain during the late
Quaternary through field investigation along the fault,measuring geomorphic deformation
and excavating trenches at some important sites.From Nanyukou to the southwest of
Shanhui,we find obviously dislocated alluvial fans,with strong neotectonic movement at
these sites.Since nearly 20ka.the vertical average slip rate is 1.55 mm/a to 2.Omm/a.
However。since nearly 6ka,it has reached as high as 2.3mm/a,which is twice that on other
segments.2 trenches were excavated around Nanyukou with 6 events discovered.The
referenced ages of the events are before 7600a.6700a~7600a,5321 a~5575a.4400a一
5400a.4200a~4400a and after 1600a B.P.with approximate recurrence interval 1400a.
The latest event is likely to be the earthquake occurring at 5 1 2 A.D..SO it is necessary to
do further work to verify this in the future.
Key words:The northern piedmont fault of the Wutai Mountain;Late Quaternary;Fault
scarp;Pale0earthquake;Slip rate
INTRoDUCTIoN
The north Wutai Mountain fault is the southern margin fault(Fig.1)of the northern part of
the Fenhe—Weihe graben basin,which starts from the Huangjia village,Yuanping in the west,
passing through Xiazhuang,E’kou,Nanyukou to the east of Xiaobaiyu.The main strike of the fault
Received on November 7,2008;revision on December 28,2008.This project was sponsored by the specific fund
for basic research and industry of Institute of Crustal Dynamics,China Earthquake administration(ZDJ2008-07,
ZDJ2007-14),co-financed by the Joint Earthquake foundation(C07028)and research and special fund for the
seismic industry(200,708,028).
Volume 24,Number 1
39。OO N
39。13 N
83
圃,圈 曰 曰 回s圆 圈 困s
回 圈-。团--田 :
Fig.1
Tectonic background of the northern piedmont of the Wutai Mountain fauh
1.Normal fault:2.Trench location;3.Alluvial fan;4.Measuring lines and serial number;5.River terrace
or alluvial terrace;6.Gully number;7.Late Cenozoic sedimentary isopach(m);8.Water system;
9.The study area;1 0.Subsidence center;1 1.Ms≥8.0 earthquake epicenter;
12.7.0≤M <8.0 earthquake epicenter(Note:map scale is the same with Fig.1(C))
is 60。NE.an山水田园诗有哪些古诗 d the length iS 85km.The fauh consists of many sub—fauhs with slight difference in
length and strikes,obliquely joining,crossing,and distributing en—echelon to one another.Its
degree of activity and size far exceeds that of the northern marginal fauh of the basin(i.e.the
Hengshan southern piedmont fault),making the basin an asymmetric graben with faulting in its
s0uth and overriding in its north.The southern wall of the fault,Wutai Mountain,with peak
Beitaiding being more than 3061 m in altitude.is nearly 2000m higher than the basin.In the Fan・
Dai fault depression basin on the northern wall,the late Cenozoic sediments have a thickness of
1 800m.with the subsidence center located on the western segment of the fault at the west of
Daixian county(Wang Nailiang,et a1.,1 996).Since the late Quaternary,under the combined
effect of a NW.trending faluh stretching into the sub—basin.a new settlement center was formed in
the eastern segment near Nanyukou(Fig.1(b)).
DEM map data from the National Science Data Sharing Project--Earth System Science Data Network(WWW
geodata.cn),satellite images from WWW.earth.google.corn
84 Earthquake Research in China
The three.1evel Tertiary planation surface developed in the northern piedmont of Wutai
Mountain(Wu Chen,et a1.,2000),while Quaternary terraces of up to 4~7 levels developed
along the transverse rivers flowing into the basin,which,together with the erosion surface of the
mountains.formed a multi.1evel stratiform geomorphie surface,indicating the intermittent dip-slip
activity of the fauh since the Cenozoic(Zhang Shimin。2007 a,2007 b.2008 a)and the most active
period in the past 20ka(Ren Junjie,et a1.,2006).According to previous studies,the northern
piedmont fault of Wutai Mountain has been characterized mainly with dip—slip and normal faulting
since the late Quaternary,with average slip rate of 0.6~0.8 mm/a along the western segment and
0.8一1.2mm/a on the eastern segment.The 512 A.D. 7.5 ea ̄hquake produced surface
ruptures on the middle part of the fauh zone.forming fault scarps of 2.Om~3.1m in height(Liu
Guangxun,et a1.,l 99 1). However,there is a lack of paleoearthquake study on the northern
piedmont fauh of Wutai Mountain. With the continuous advances ifl exploratory trenching
technology and pale0seism0logy in the past ten years(Seih,1978;Ding Guoyu,1982;Schwartz,et
a1.,1984;Deng Qidong,1984;Mao Fengying,et a1.,1995;McCalpin,1996;Ran YonIgkang,et
a1.,1997,1999;Xu Xiwei,et a1.,2000;Ran Yongkang,2001;Zhang Peizhen,et a1.,2003;Zhang
Shimin,2008b)and in dating technology(Aitken,1985;Chou Shihua,1997;Guo Zhiyu,1998;
Jiao Wenqiang,1998;Murray,et a1.,2000;Chen Shu’e,et a1.,2003;Jia Yaofeng,et a1.,2005),
as well as topographic measurement techniques(Sun Arts,1989;Chen Junyong,1998;Hu
Jianguo,et a1.,2002;Dang Yamin,et a1.,2006;Ren Zhikun,et a1.,2007),it is necessary to
recalculate the late Quaternary slip rate of the fault.In recent years we focused on the survey of
the Late Quaternary fauh landform along the segment near Nanyukou,excavated two trenches of
10m in depth and obtained more accurate fauh slip rate and paleoearthquake data.
1 oFFSET ToPoGRAPHY
J.1 Fault Scarp and Fault Facet
In the area near Nanyukou,the offset landform of the northern piedmont of Wutai Mountain
fault appears mainly as fault scarp,fault facet and alluvial terrace scarp.In the 4500m-long
piedmont from the west of Nanyukou to zhongzhuangzhai village(Fig.2(a))and the 1500m-long
piedmont on the east of Shanhui(Fig.2(c)),the gullies are large,and with developed piedmont
alluvial fans.The gullies in the mountain pass show strong orographic effect and the mountainous
area remarkably retrograded,forming the latest fault scarps composed of alluvial terraces in the
piedmont.These alluvial terraces correspond to T2 terrace within the gullies(Fig.2).
To the west of Nanyukou,the top of the fault scarp at front of alluvial terrace is 20m~30m
above the depressions between the fan terraces(Fig.3.Table 1).Under the strong control of
piedmont fault activities,the top of these alluvial fans extend along the fault zone,with a steep
slope and a height difference of up to 50m from the fan top to the edge.The fan slope reaches
4。~5。,and the fan roof 20m~35m above low—lying land.In the gully,H0,at the south of
Nanyukou,the stratigraphic sequences of the alluvial terrace from top to bottom are listed as
follows(Fig.4):
(1)Sallow plough horizon,loose structured,plant roots developed.Thickness:O.2m.
(2)Gray—black black loam(S0),granular—clump structured,loose,plant roots and white
calcium membrane,and the color becomes lighter with depth.Thickness:1.3 m.
(3)Grayish yellow Malan loess(L1),vertical joints developed,color becoming lighter with
depth;the upper part consists of lumps,dark grayish yellow,transitioning from the overlying black
solid loam(S0).OSL dating of the samples from the bottom of the layer yields the age of 1 9.1
Volume 24,Number 1 85
Fig.2
Fault scarp geomorphology of the northern piedmont of Wutai Mountain fault
T2 is the river’S second-level terrace,R 5~R10,H1~H3 are gully number
E W
Fig.3
Measured fault scarp profile in front of the Late Quaternary alluvial terrace
a~h are the measurenlent line numbers,the measurenlent line position is ShOWn in Fig.1(C);T2 is the
second—level terrace and the contemporaneous alluvial terrace:“22m”is the scarp height
1.Oka B.P.Thickness:1.7m.
(4)Mottled alluvial sand gravel layer with a thickness>20m,where the gravel is composed
of gneiss,horizontal bedding developed;the gravel is poorly sorted,angular to sub—angular in
86 Earthquake Research in China
shape,2cm一30em in diameter.The basin level tilts with a plunge of 5。or so;the gravel layer is
mixed with loess.1ike soil of a thickness leSS than 1.0m locally.
Quaternary aeolian dust accumulation developed in the study area.Loess of varied
thicknesses accumulated on the geomorphie surfaces at various levels.After the top surface of the
terrace or alluvial fan was free of water flow(i.e.。above the flood leve1),the top began to hold
the loess.Loess consists mainly of silt particles and drifts before sedimentation and thus Call be
fullv exposed.In optical luminescence dating.they are obviously better than the alluvial and
pluvial deposits.Thus,the TL age of the basal of the grayish-yellow soil layer is roughly equal to
the formation age of the terrace surfaces.The piedmont alluvial terrace of the Nanyukou gullies
toward the upper stream corresponds to terrace T,.At the section of the Yangyan River outside
the mountain pass in the east of gully H0,the top of terrace T2 is 18.70.9ka B.P.by dating
(see below).According to the 1 995 Xinding research group of Institute of Crustal Dynamics of
China Seismological Bureau investigation of the eastern segment east of Jingcun village,about
45kin west of Nanyukou a dark brown paleosol layer was found to be intercalated at the bottom of
the Malan loess overlying the alluvial terrace,with a“C age of(22.8720.507) ka.Therefore,
in accordance with the OSL dating result of its overlying loess or the bottom of the paleosol,the
formation of the alluvial fan is inferred to be 19~22ka B.P.
From Dongshan to Huishan is a 1900m.1ong bedrock foothil1.where obvious fault scarps and facets
have formed(Fig.2(b)). e gullies are small in size,and piedmont alluvial fans undeveloped.In the
piedmont,composite fault scarps composed of bedrock have developed(Fig.2(b)).
Table 1 The vertical displacement amount and slip rate of the northern piedmont of Wutai
Mountain fauh
Note:①Ontemporaneous soil is not yet seen on the top surface at the depth of 10m underground in trenches R,
and H1,so in this Table,the amount of vertical displacement is the fault scarp height plus lOm.②The vertical
slip rate in this Table is the average slip rate since 20ka
On the southeast of Shanhui.the piedmont alluvial terraces have a similar stratigraphic
structure.The piedmont alluvial terraces corresponding to Terrace T constitute the latest fault
scarp,with its top 20m above the low—lying lands between piedmont alluvial fans(Fig.1,Fig.3,
Table 1).
Atier one side of the alluvial terrace was deposited in the basin.it was covered by the latter
sediments.and the top interface of this stratum was not seen at the depth of 10m underground in
trench R7 and H1(Fig.1(c)).Therefore,the vertical displacement should be 10m over the height
Xinding Research Group,Institute of Crustal Dynamics,China Seismological Bureau,1995.Final report on the
study of active fau纳兰容若的爱情诗词 lts and ea ̄hquake risk in Xinding Basin一“1:50000 scale geological mapping and
comprehensive study of active fault of Xinding Basin”.
Volume 24,Number 1 87
Fig.4
Alluvial terrace profile in the Gully H0 at the south of Nanyukou village
(see Fig.1 for location of H0)
1.Malan loess;2.Loess—like soil;3.Paleosol;4.Gravel layer;5.Gneiss;6.Sampling site;7.Fault
of the fault scarp.According to the above dating results,the contemporaneous geomorphic surface
generally formed in 20ka B.P.,thus,the average slip rate of the Nanyukou segment of the
northern piedmont of Wutai Mountain fault is estimated to have been no less than 1.55 mm/a~
2.0mm/a since 20ka(Table 1).
J.2 Offset Terraces
Under the influence of normal dip—slip faulting,a series of horizontal gullies have developed
in the Nanyukou area in the northern piedmont of Wutai Mountain.0ur survey found that both
rivers and gullies were offset at the mountain exit,and the contemporaneous deposits on the
downthrown block were buried.With the aid of virtual differential GPS techniques,we obtained
the topographical measurements at sub-meter level accuracy,thus making quantitative analysis of
the river’s longitudinal profile possible. Generally,the 9200 portable virtual differential
measurement system,manufactured by Nanfang Sur杨绛简介 veying and Mapping Instrument Company,has
a measuring accuracy of 1ess than 50cm under good signal conditions in the field.
The Yangyan River originates east of Wutai Mountain,its origin cutting into the planation
surface of the Beitaiqi period.It flows northward between Nanyukou and Dongshan into the basin
(Fig.1),with a total length of 18.5km,seven terrace levels developed in the mountainous area
(Zhang Shimin,et a1.,2007a),and the contemporaneous deposits on the terrace were buried in
the other side of the basin.
Terrace T1 mainly distributes to the east of Yangyan River,and the valley is long and narrow,
on which the asphalt road from Dongshan village to Wutai Mountain was built.The terrace is an
accumulative terrace,the width of the terrace surface is about 100m.and the top is 4.2m above
the river leve1.The bottom of the terrace is the gravel layer with a visible thickness of 1.0m.The
stratum overlaying the gravel layer is floodplain facies,gray—black sand,mainly fine sand,calcite・
cemented.TL dating of samples from the bottom of the layer shows an age of 5.980.51ka B.P.
In the gully H6 on the west side of Nanyukou,the paleosol on the top of gravel layer of terrace Tl
has an age of 576545ka B.P.by C dating.Therefore。terrace T.maybe formed in 6ka B.P.
From terrace T to the northern piedmont fault of Wutai Mountain,the north wall of the fauh
disappears,buried by the modern alluvial fans(Fig.1,Fig.5).
Terrace T2 is on the west bank of Yangyan River,where Nanyukou village and Shuimo village
are located.It is an accumulation terrace with strata structure similar to that of the alluvial terrace
of gully Hn.Above the dual structure are 1.Om thick loess Lf and 1.5 m thick black loam Sn.The
bottom of loess L.has an OSL age of l8.70.9ka B.P.。which is the age of dehydration of the
E、co孑∞>∞卫
88 Earthquake Research in China
0 500 1000 l500 2000
Fig.5
Terrace’S longitudinal profile map of Yangyan River(see Fig.1 for river location)
ground,and may be taken as the approximate age of terrace formation.We infer that the terrace
surface has a height of 1 6m above the river at its front edge about 20m south of Nanyukou village,
while its back edge connects to the alluvial terrace at the west of Nanyukou.The fault zone
roughly crosses the stone bridge between Dongshan to Nanyukou.Near the central part of the
Nanyukou village on the south,the pediment edge of terrace T2 is 20m above river level,indicating
the tilting effect of the fault.Due to the movement of the northern piedmont fault of Wutai
Mountain,the contemporaneous deposits on the downthrown block are buried.
Gully R5 is on the east of the Yangyan River(Fig.1),and along the reach on the upthrown
block,three—level terraces and 1 1一level knickpoints of various sizes have developed(Fig.6).
Fig.6
The longitudinal profile of gully R5(for gully location,see Fig.1)
Virtual deferential GPS measurement was done for river・bed and terrace,with the error less than 0.5m;
mountain ridges were read from 1:10000 scale topographic map;contour interval 5m
Tl disappears at the knickpoint 1,which is 4.5m high,at the distance about 13m upstream.
At 28 m upstream,T2 disappears at knickpoint 2,which is 6.7 m high.From the bottom part
of the vanishing point of the terrace to the outlet of the river,the valley is relatively narrow.
Upstream from the vanishing point of terrace is a 23 m-long subcritical flow section,and the valley
is relatively wide.
姗 瑚 抛 瑚
1 l l l l I
g,Ⅱ0_lj 姗 抛 瑚 1 1 1 1 l —篇、g 葛
Volume 24,Number 1 89
At the distance of 57 m upstream,T disappears at knickpoint 6.Downstream from the
vanishing point of the terrace is a 7 m-long supercritical flow section consisting of three knickpoints
with heights of 1.5m.1.5m and 6.0m。and the valley is narrow.The upstream from the vanishing
point of the terrace is the subcritical flow section.the valley is wide and a number of knickpoints
of various levels with a height less than 1 m have developed.
Trenches were excavated at the mountain exit,which reveal the alluvial facies sandy gravel
layer contemporaneous with terrace Tl at a depth of 9.5 m and below,indicating the ve ̄ical
displacement of the fault since the formation of T,is up to 14m.In the bottom of its overlying,
abundant carbon bars are buried,with C dating age 469070a B.P.,and calendar age 5321a~
5575a B.P.Combined with the dating results of gully H6,the age of terrace Tl is estimated as
6ka,thus the fault slip rate is 2.3mm/a since 6ka.
2 PALEOEARTHQUAKE TRACES
2.J Paleoearthquakes Exposed in Trench R7
Trench R,is located at the foot of slope of alluvial terrace T,on the right side of gully R7
(Fig.1),roughly perpendicular to the fault strike,with a width of 8m,a depth of 9m or so,and a
length of 25 m.The upthrown block revealed by the trench is the alluvial strata in the lower part of
the T2 terrace.The era of downthrown block is relatively new.From the fault zone outward are
colluvial grayish—yellow loess—like soil and the accumulative alluvial fan of gully R7(Fig.7,
Fig.8),The four colluvial wedges D I~D4 revealed by the trench are vertically stacked,
indicating four paleoearthquake events,among which the top of colluvial wedge D4 was ̄rmed in
the latest fauh activities,with no displacement across fault observed.
Stratigraphic sequences from the bottom up are as follows:
Layer(1):Gray—yellow breccias mixed with soil.The breccias are 5 cm~1 5 cm in diameter
and show certain preferred orientation in their arrangement under the impact of fault activity.Soil
is fine sand.The visible thickness of the layer is 1.5m.
Layer(2):Gray—yellow l龃龉龌龊的读音 oess,pure quality without bedding and sandy grave1.The structure
is uniform and solid.Visible thickness is 1.5m.
Layer(3):Loess colluvial layer(colluvial wedge D 1),wedge—shaped,maximum thickness 0.
8 m,consisting of grayish yellow soil mixed with black—gray clods in loess.The latter is 3 cm~
t0cm in diameter,containing a small amount of breccia.
Layer(4):Brown—black paleosol(P1),a gradual transition to the underlying strata,with
clear delineation of the overlying strata.Thickness:0.4m.The“C dating age of its top is 6790a
_
-4-90a,and calendar age is 7568a~7715a.
Layer(5):Colluvial grayish—yellow loess-like soil,loosely structured,consisting of a mixture
of grayish—yellow loess and yellow—grayish loess,with clods of the latter being 3cm~10cm in
diameter.The layer contains dark gray clods with a diamete浮云游子意落日故人情 r of 1 cm一3 cm,and fine grave1.The
thickness of the layer is 0.4m~0.7m.and near the fault it increases to 1 m.
Layer(6):Gray gravel soil,0.2m~0.4m thick,thickening near fault,being of talus facies,
undeveloped bedding.
Layer(7):Colluvial facies grayish—yellow loess—like soil,composed of grayish—yellow loess
mixed with dark gray clods,which have a diameter of 5 cm~20cm,bearing fine—grained grave1.
The thickness is 1.0m~1.5m and increases near the fault.Layer(5)and layer(7)constitute
Earthquake Research in China
囡t囤z团,囡 田s回 囡 回s
Fig.7
Cross.section of the east wall of Trench R7
1.Gravel;2.Gray clods;3.Normal fault;4.OSL sampling points;5.“C sampling points;
6.Colluvial wedge number:7.Paleosol layer number;8.Stratum number
bedding.Thickness:0・2m・
.. Layer(9):Dark—gray paleosol(P2),containing breccia.Thickness:0.1 m~0.2m. C
dating age is 592070a.and the calendar age is 6664a~6845a B.P.In the west wall of the
trench,the C dating age is 637045a.
Layer(10):Colluvial facies gray—yellow clods mixed with loess—like soil(colluvial wedge
D ),the diameter of gray clods is 5cm~10cm,fine gravel diameter is 2cm~30cm,fine gravel
content is 5%to 20%.undeveloped bedding.Thickness:0.4m~0.5m.
Layer(1 1):Brown—gray paleosol(P3),containing fine—grained gravel(5%)with the
diameter of 2cm~7cm.。 C dating age of its top is 448070a B.P..and the calendar age is
4983a一5287a B.P.The layer was offset by the latest fault activity.
Layer(1 2):Dark grayish—yellow loess-like soil,containing fine—grained gravel with a content
of 5%and a diameter of 2cm~5cm.Thickness:1 m.
Layer(13):Dark grayish yellow loess—like soil,containing breccias,showing weak
pedogenesis.Thickness:O.3m.
Layer(14):Talus facies gray sand and gravel layer,gravels are angular shaped and mainly
2cm~4cm in diameter.Content of silt grain size is below 20%.
Layer(15):Colluvial grayish—yellow loess—like soil mixed with yellow-gray clods and breccia
(colluvial wedge D4),breccia is rich near the fault(see Fig.8).Thickness:1.4m.
Volume 24,Number 1
Layer(1 6):Pluvial sand and gravel layer,horizontal bedding,fairly well sorted.Gravels are
5~50cm in diameter,angular and sub.angular shaped.Thickness:6.5m or 8o.
Layer(1 7):Gray pluvial grayish—yellow sandy gravel layer intercalating loess-like soil,
horizontal bedding developed,fairly well soaed.Gravels are 2cm~40cm in diameter,angular and
sub—angular shaped.Visible thickness:12m.
Colluvial wedges D】~D4 indicate 4 seismic surface slip events.The maximum heights of
colluvial wedges are different,1.5m,4.0m,1.5m,1.8m,successively. Its sedimentary
characteristics are slightly different.Directly above D1 and D3,paleosols have developed,but no
talus bedding.Colluvial D,intercalates sand and gravel layer。with talus bed and paleosol
developing at the top.Only colluvium was developed in D4,and soil has not yet formed at the top.
According to the results of“C dating,event D1 occurred before 7600a B.P.,event D,between
6700a一7600a B.P..and event D,between 5100a~6700a B.P.The time span of paleosol
development on the top of D3 should be less than the difference between ages of the underlying
paleosol and the top surface.that is not more than 1600a.We take 1600a as the maximum time
limit for the remarkable pedogenesis of the top of the colluvial wedge.and in view that the soil has
not formed yet at the top of D4,we deduced the age of the event D4 to be less than 1600a.Since 5 12
A.D.the region has not been hit by other big ea ̄hquakes.and the trench is only about 20km from
the surface rupture zone of the 512 A.D.earthquake as determined by previous researchers(Liu
Guangxun,et a1.,1991),it is likely that event D4 is possibly the 512 A.D.ea ̄hquake.
Fig.8
Cross-section of the west wall of R7 trench
2.2 Paleoearthquake Revealed in Trench R5
Trench R5 is located near the exit of gully R5(Fig.1),ve ̄ical to the fault zone,with a length
of 20m,depth 9.5m,width 4.0m at the top and 2.1m at the bottom.The footwall of the fault is
the green.gray plagioclase amphibolite of the Wutai group of Archean Eon.The trench reveals
four alluvial cones A1~A4 stacked from top to bottom(Fig.9),possibly representing the rapid
accumulation at the gully exit after the 4 seismic events.Each alluvial cone consists of a sand
92 Earthquake Research in China
gravel layer,pooHy sorted and without rounding at the bottom,similar to cotluvia.The alluvial
cone is directly separated by a fine—grained loess layer,the latter of which may be the result of the
transformation of aeolian dust deposits eaused by surface flow or runoff during the major
earthquakes.The top of the alluvial cone A4 was formed after the fault latest activity.No
displacement has been observed across the fault.
Stratigraphic sequences of the hanging wall of the fault from bottom up are as follows(Fig.9):
Layer(1):Gray—white alluvial sand gravel layer,with visible thickness 0.4m on the east wall
of trench and 1.0m on the west wal1.Gravels are mainly sub—rounded and rounded with diameters
of 5cm一50cm.The sand is pure in quality,horizontal bedding.
Layer(2):Alluvial cone A1,a grayish—yellow sand gravel layer mixed with soil,wedge-
shaped,with a height of 1.2m,length 4.Om.The lower part is composed of black amphibolite
breccia mixed with gray—yellow sand.The breccias are 4cm~40cm in diameter,0.6m thick,
2.0m long,unstratified,unsorted,with no preferred orientation in their arrangement,and the
bottom is rich in carbon rods with“C age 4690a70a B
.P..and calendar age 5321 a~
5575 a B.P.The breccias in the upper part of alluvial cone show a certain orientation in their
arrangement along the slope surface,and laminated sand layer is developed along the slope.The
layer towards the foot of the slope connects to the brown—gray paleosols P1.
Layer(3):Brown—black,brown—gray paleosol P1,0.4m~0.5m thick,with the lower part
darker in color,containing carbon particles,which are sandy silt or clayey silt,containing fine
gravel,undeveloped bedding。gradually transitioning to the overlying grayish—yellow loess-like soils.
Layer(4):Gray—yellow loess-like soil,0.4m~0.6m thick,consisting of pebbly sandy silt,a
mixture of aeolian talus deposits containing carbon rods and carbon particles.A thin sand layer
has developed near the fault,and gravel content is slightly increased.
Layer(5):Alluvial cone A2.1’an interbed of gray sandy gravel and soil,with a height of 1 m
and length 3 m,unstratified and un—sorted in the lower part,and in the upper part,with preferred
orientation in the arrangement along the slope direction.Bedding can be slightly seen.
Layer(6):Brown—gray paleosol P2_l'0.2m thick,composed of sand gravel and silt.
Layer(7):Gray—yellow soil mixed with sand gravel A2_2,0.35m thick,unstratified and
unsorted.
Layer(8):Brown—gray paleosol P2.2,0.2m thick,composed of sand gravel and silt.
Layer(9):Gray・yellow sand gravel layer mixed with soil A2_3,1.0m high and 3 m long.In
the lower part,bedding is not developed;at the upper,breccia is aligned along the slope and
bedding is slightly visible.
Layer(10):Brown-gray paleosol P2_3,0.1m一0.3m thick.It thins near fault,the development
level gets lower and the color turns yellow—gray.The C dating age is 385070a B.P..and the
calendar age is 4157~4406a B.P.
Layer(1 1):Gray-yellow sand gravel mixed with soil A24,0.3m一0.4m thick.The gravel is
aligned along the slope,but with no significant stratification.Away from the fault,the facies
changes to grayish—yellow loess—like soil.
Layer(1 2):Brown—gray paleosol P2_4,0.3 m~0.4m thick,including breccias aligned along
the slope direction.Away from the fault,the gravel content gets lower,there is no preferred
orientation in their arrangement and no bedding.
Layer(13):Gray-yellow loess-like soil,0.4m~4.5m thick.The layer is thinnest near the
fault,and the gravel content increases slightly.Bedding is not developed.It shows mainly aeolian
accumulation,associated with talus deposition.Among them,the upper layer shows a horizontally
facies-changing relationship with layer(14)and layer(20),respectively.
Layer(14):Gray-yellow sand gravel mixed with soil,1.2m thick,which,together with layers
Volume 24,Number 1 93
(1 5).constitute the 1.5 m—high,6.5 m—long alluvial cone A3.Its lower part consists of breccias
mixed with loess-like soil.and away from the fault,gravels are aligned along the slope.The upper
Dart is formed with smaller diameter gravels and sand,aligned along the slope.The age of central
part is 4.20.5 ka B.P.by optical luminescence dating.
Laver(15):Brown.gray paleosol,0.2m~0.3m thickness,consisting of sandy silt,containing
fine grave1.The layer develops above the alluvial cone A3 near fault and on the top of loess—like
soil away from the fault.
Laver(1 6):Aeolian,talus facies grayish-yellow loess—like soil,horizontal bedding
developed.1.5m thick.On its top is weakly developed a 0.2m—thick yellow—gray paleosol,
granular structured.The layer iS offset by the latest faulting.
Layer(1 7):Alluvial cone A4,1 m high and 4m long,consisting of loose structured grayish—
ve11ow loess-like soil mixed with breccia,undeveloped bedding,the content of breccia is 1 0%,and
there is no preferred orientation in the arrangement.
Laver(1 8):Gray-yellow diluvia1.alluvial sand gravel mixed with soil,0.4 m thick,composed
0f breccia.sand and grayish.yellow silt soil,horizontal bedding developed,unso ̄ed.
Laver(19):Gray-ye1low loess—like soil intercalating thin gravel layer,0.6m~1.5m thick.
The loess-like soil is mixed with breccias,with no significant horizontal bedding developed.There
is horizontal bedding developed in the sandy gravel interbed.
Laver(20):Alluvia1 sandy gravel lenticle,horizontal bedding developed,content of the grain
size under silt is less. Gravels are angular—and sub—angular shaped with a diameter of 2 cm~
40cm in genera1.The lenticle is thinned out towards the direction of gully R5 and is inferred to be
the diluvium of the gully on its west.
Bedding is poorly developed in alluvial cones A 1~A4,where the lower part lS composed
固 团。囡,田 因s囤s固
Fig.9
Cr0ss—section of the east wall of trench at gully R5
1.Gravel:2.Normal fault;3.OSL sampling points;4.“C sampling points;5.AlluVial coHe numbe ;
6.The paleosol layer number;7.Stratum number
a
94 Earthquake Research in China
certain extent;the top has been subject to pedogenesis,and strata configuration carries the general
characteristics very much like the colluvial wedge.Gully R5 is small in scale,with a large gradient
in the upper reach,so provenances are difficult to deposit on the river bed,even on the gully bed
of the last glacia1.There is no evidence of aggradation(Zhang Shimin,2007 a),only the erosion
terraces developed.The alluvial cones revealed by the trenches indicate several stages of material
transportation and rapid accumulation since the mid—Holocene,which are likely the surface
response after earthquakes.The gully wall collapse and surface ruptures caused by earthquakes
provided the provenance and the earthquake fault scarp provided the potentia1.Substances were
transported in short distance by flood to the gully outlet and quickly stopped and deposited,
forming alluvial cones similar to colluvium and deluvium.Alluvial cone Al,A3,and A4 represent
three rapid accumulations since 5.6ka,probably the follow—up fluvial accumulations of the three
earthquake events(event Al,A3,and A4).The fine—grained loess—like layer may be the
transformation of aeolian dust deposits by the surface flow or runoff between the large earthquakes
(called inter—earthquake accumulation in the article).Sand gravel layers A2一l~A2_4。are
consecutively stacked together,and there are almost no inter—earthquake fine-grained
accumulations between each other,morph0logically forming the composite alluvial cone A2.
According to the result of dating,the composite alluvial cone formed between 4400a to 5400a over
a total time span of 1 000 a.And according to the historical seismic activity background in the
Fenhe-Weihe graben system,it is unlikely to be the follow—up fluvial accumulation due to the four
paleoearthquake events recurring in・situ,but more likely the result of accumulation of four floods
after a large earthquake(i.e.,the event A2).However,more reasoning is needed to verify this by
more precise dating.According to the measured ages of strata in the trench,event Al occurred
between 5321a~5575a B.P.,event A2 occurred between 4400a~5400a B.P.,A3 occurred
between 4200a~4400a B.P.,and A4 occurred after 4200a B.P.Considering that paleosol has not
developed at the top of A4,it may be younger,probably the surface response to the 512 A.D.
earthquake.
2.3 The Sequence of Paleoearthquake Events
Under a comprehensive analysis of the two trenches,the events D1 and A l may be the same
event,and events Dd and A d may be the same event.Thus。the trenches revealed a total of six
events,that is,Dl,D2,D3(or A1),A2,A3 and D4(or A4),with occurrence times before
7600a 清明节诗词 B.P.,6700a~7600a B.P.,5321a~5575a B.P.,4400a~5400a B.P..4200a~4400a
B.P.and 1600a B.P.,successively(Table 2).With the median of the ages as the reference
value,we obtain the recurrence intervals of the latest 5 events as 1700a,550a,600a and 2800a,in
succession.and the average is about 1400a.
Table 2 The pale0eanhquake catalog on the northern piedmont fault of Wutai Mountain since
the late Quaternary
Volume 24,Number 1
3 SUMMARY AND DISCUSSION召公谏厉王弭谤原文及翻译注释
95
The northern piedmont of Wutai Mountain fault is the southern margin fault of the Fandai
basin in the Fenhe・Weihe graben.Along the Nanyukou segment,the fault shows strong late
Quaternary activity.The late Quaternary alluvia】fans formed fault scarps up to 20m~30m.Since
the last 20ka.the average fault slip rate is not less than 1.55~2.0mm/a,and since the last 6ka,
the slip rate is up to 2.3 mm/a,nearly twice the average slip rate of the other segments of the fault
(Liu Guangxun.et a1..1991).
Two trenches on the Nanyukou segment of the northern piedmont of Wutai Mountain fault
revealed six paleoearthquake events in total,with referenee ages before 7600a,6700a~7600a,
5321 a~5575a.4400a~5400a.4200a~4400a and after 1600a,and an average recurrence
interval is about 1400a.The latest event is most likely the 5l2 A.D.earthquake。but further
dating work is required for verification.Considering that events A2 and A3 are indirectly identified
through debris cones rather than the direct identification through colluvial wedges in front of
scarps,there is uncertainty.Thus it is also subject to further validation by trenching.
Much oDtical luminescence dating has been performed on the colluvial deluvia1 deposits in
the two trenches.However it appears the majority of the age data is inverse,and far away from
fheHC dating resuhs
.
so they have not been fully adopted.The technica1 problems in it remain to
be studied further.
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About the Author
Ding Rui,born in 1 982,holds a Masters degree,with major research interests in the area of
active tectonics and earthquake engineering.E—mail:Reiding@hotmail.eom.
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