场地划分标准对基岩地震动参数衰减关系的影响王珊;张郁山;尤贺【摘要】基于美国NGA强震观测数据库中描述场地的不同指标,定义了五种不同的“基岩”场地类型,得到了相应的数据集;同时采用最小二乘法回归得到了世界范围内对应不同“基岩”定义的地震动参数衰减关系,并研究了不同场地划分标准造成的基岩地震动参数衰减关系的差异.【期刊名称】《震灾防御技术》【年(卷),期】2014(009)004【总页数】11页(P759-769)【关键词】NGA强震观测数据库;地震动衰减关系;峰值加速度;反应谱【作者】王珊;张郁山;尤贺【作者单位】中国地震灾害防御中心,北京100029;中国地震灾害防御中心,北京100029;北京工业大学材料学院,北京100022【正文语种】中文地震动是引起震害的外因，是工程地震研究的主要内容。
地震动的特性十分复杂，为了研究与工程应用的方便，通常采用对特定地震动参数（主要指对工程结构地震反应有重要影响的参数，如幅值、频谱和持时等）进行研究的方法来开展探索。
以现有的强震观测记录为基础，使用经验模型，采用统计的方法得到地震动参数衰减关系，是地震动参数研究和工程应用中一种常用的方法，也是地震危险性分析工作的基础。
美国太平洋地震工程研究中心（Pacific Earthquake Engineering Research Center，简称PEER）的NGA（Next Generation Attenuation）项目的主要目标，是建立新的地震动衰减关系模型。
针对该目标，NGA通过对已有PEER强震数据库的修订、补充、整理，已经形成目前国际上最为完整、先进的强震数据库。
利用该数据库提供的强震观测记录，NGA不同研究小组（Abrahamson等，2008；Boore等，2008；Campbell等，2008；Chiou等，2008；Idriss，2008）已建立了世界范围内地震动参数的衰减关系。
但是，这些基于NGA数据库的衰减关系并不能直接应用于我国的工程实践，其主要原因在于：①NGA衰减关系使用的地震参数（包括震级、震源机制等）和场地参数（包括断层距、剪切波速、盆地参数等）与我国常用的模型不同，且模型复杂，计算不便；②不同地区地震动衰减可能存在区域性差异，统一采用世界范围的衰减关系不能反映我国不同地震区地震环境的差异。
第一、二章地震的基础知识1、世界地震分布的主要集中区域是什么？环太平洋地震带、欧亚地震带、大洋海岭地震带2、地球内部的基本构造是什么？地壳（数千米至数十千米、岩石）、地幔（上、下地幔、岩石和软流层）、地核（外核、内核）3、4、5、从地震成因、地震序列、震源深度上划分，地震类型主要有哪些？（构造、火山、陷落、诱发）（主震余震型、震群型、单发型）（浅源、中源、深源）6、构造地震发生的宏观背景是什么？板块的构造运动7、简要叙述地震发生机理的弹性回跳说。
地壳由弹性的、有断层的岩层组成；地壳运动产生的能量以弹性应变能的形式在断层中长期积累；当弹性应变能积累及其岩层变形到达一定程度时，断层上某一点的两侧岩体向相反方向突然滑动，弹性应变能释放，产生地震，发生变形的岩体又重新恢复到，没有变形的状态。
8、简要叙述地震发生机理的粘滑说。
每一次断层发生错动时，只释放了积累的应变能中的一小部分，而剩余部分则被断层面上很高的动摩擦力所平衡，地震后，断层两侧仍有摩擦力使之固结，并可以再积累应力而发生较大的地震。
9、什么是震级，一般如何定义？震级是表示一次地震大小的指标，是地震释放能量多少的尺度。
一般以地震仪记录的水平方向地震波最大位移的平均值来测定震级的大小。
10、什么是烈度？震级和烈度有何关系？烈度是某一区域范围内地面和各种建筑物受到一次地震影响的平均强弱程度的一个指标。
一次地震只有一个震级，烈度则随地而异。
11、什么是烈度衰减规律？描述烈度随震级和距离变化而改变的统计规律。
实际地震烈度的分布并不十分规则，通常取圆形等震线拟合和椭圆形等震线拟合两种类型。
12、地震波有哪些类型？体波（纵波、横波）、面波（瑞利波、乐夫波）13、什么是纵波、横波，它们的传播速度有什么差异？试从弹性波动方程的角度进行推导。
质点振动方向与波的传播方向一致的为纵波，质点的振动方向与波的传播方向正交的为横波。
波动方程具有同样的形式，但是系数不同，P34,3514、地震动各分量主要由什么波产生的？体波产生水平和垂直分量，面波产生转动分量。
GEOPHYSICS,VOL.66,NO.1(JANUARY-FEBRUARY 2001);P .78–89,9FIGS.Case HistoryThe use of geophysical prospecting for imaging active faults in the Roer Graben,BelgiumDonat Demanet ∗,Fran¸c ois Renardy ∗,Kris Vanneste ∗∗,Denis Jongmans ‡,Thierry Camelbeeck ∗∗,and Mustapha Meghraoui §ABSTRACTAs part of a paleoseismological investigation along the Bree fault scarp (western border of the Roer Graben),various geophysical methods [electrical profiling,elec-tromagnetic (EM)profiling,refraction seismic tests,elec-trical tomography,ground-penetrating radar (GPR),and high-resolution reflection seismic profiles]were used to locate and image an active fault zone in a depth range between a few decimeters to a few tens of meters.These geophysical investigations,in parallel with geomorpho-logical and geological analyses,helped in the decision to locate trench excavations exposing the fault surfaces.The results could then be checked with the observations in four trenches excavated across the scarp.Geophysical methods pointed out anomalies at all sites of the fault po-sition.The contrast of physical properties (electrical re-sistivity and permittivity,seismic velocity)observed be-tween the two fault blocks is a result of a difference inthe lithology of the juxtaposed soil layers and of a change in the water table depth across the fault.Extremely fast techniques like electrical and EM profiling or seismic refraction profiles localized the fault position within an accuracy of a few meters.In a second step,more detailed methods (electrical tomography and GPR)more pre-cisely imaged the fault zone and revealed some struc-tures that were observed in the trenches.Finally,one high-resolution reflection seismic profile imaged the dis-placement of the fault at depths as large as 120m and filled the gap between classical seismic reflection profiles and the shallow geophysical techniques.Like all geo-physical surveys,the quality of the data is strongly de-pendent on the geologic environment and on the contrast of the physical properties between the juxtaposed for-mations.The combined use of various geophysical tech-niques is thus recommended for fault mapping,particu-larly for a preliminary investigation when the geological context is poorly defined.INTRODUCTIONThis paper describes the application of various geophysical prospecting techniques to locate and image Quaternary fault zones as part of a paleoseismological project (Meghraoui et al.,2000).Paleoseismology aims to determine the Late Pleistocene and Holocene history of near-surface faulting often associated with large earthquakes.This usually requires the excavation of shallow trenches across the trace of the suspected active fault.Active normal faults exposed at the surface are usuallyPublished on Geophysics Online July 11,2000.Manuscript received by the Editor March 22,1999;revised manuscript received June 15,2000.∗Liege University,LGIH,Bat B19,4000Liege,Belgium.E-mail:ddemanet@ulg.ac.be.‡Formerly Liege University,LGIH,Bat B19,4000Liege,Belgium.Presently LIRIGM,Universite Joseph Fourier-Grenoble 1,BP 53,F 38041Grenoble Cedex 9,France.E-mail:djongmans@ulg.ac.be.∗∗Royal Observatory of Brussels,av.Circulaire 3,1180Brussels,Belgium.§CNR-CS,Geologia Tecnica,via Eudossiana 18,00184Rome,Italy.c 2001Society of Exploration Geophysicists.All rights reserved.expressed in the topography as fault escarpments.However,in intraplate areas characterized by relatively low rates of tec-tonic deformation,the geomorphic expression of an active fault may be very subtle as a result of the complex interplay among tectonic,depositional,and erosional processes or intensive agricultural exploitation.However,nondestructive geophysi-cal prospecting techniques may be applied to map the near-surface fault trace with great accuracy.In the last few years,a large number of high-resolution seismic reflection surveys have been conducted (e.g.,Williams et al.,1995;Palmer et al.,1997;78Imaging Active Faults79Van Arsdale et al.,1998)to provide information on Quater-nary fault geometry and timing.For very shallow investigation, ground-penetrating radar(GPR),which can bridge the gap be-tween high-resolution seismic surveys and trenching,has been applied by Cai et al.(1996)in the San Francisco Bay region. At the border of Nevada and California,Shields et al.(1998) have used several geophysical techniques(seismic reflection, magnetics,and electromagnetics)to locate the extension of the Parhump Valley fault zone.This paper presents the results of a geophysical campaign performed in the Bree area(Roer Graben,northeast Belgium)as a reconnaissance tool prior to trenching,which included refraction seismic records,electro-magnetic(EM)and electrical profiling,electrical tomography, ground penetrating radar(GPR),and high-resolution seismic reflection profiles.The foremost aim of this investigation was to determine the exact position of an active fault to precisely locate a subsequent trench.A second objective was to image the fault zone at shallow depths,therby allowing a direct com-parison with trench data and hence a confident extrapolation of direct observations to greater depths.GEOLOGICAL SETTING AND TECTONIC ACTIVITY The Roer Graben,which crosses three countries(Belgium, The Netherlands,and Germany),is bounded by two north–northwest,south–southeast-trending Quaternary normal fault systems(Figure1).The eastern boundary is defined by the Peel boundary fault,where the5.4-M W1992Roermond earthquake occurred(Camelbeeck and van Eck,1994);while the western boundary is defined by the Feldbiss fault zone,which is partially located in Belgium.Evidence of tectonic activity in the Roer Graben is given by(1)the strong subsidence during the last 150000years(Geluk et al.,1994),(2)the Quaternary faults and their associated morphology along theflanks of the graben, (3)the0.8–2-mm/yr vertical rate of deformation obtained by the comparison of levelings during the last100years(Van den Berg et al.,1994;M¨alzer et al.,1983),and(4)the present-day seismic activity(Camelbeeck and van Eck,1994).For the Feldbiss fault zone,tectonic activity is mainly indi-cated at depth by seismic profiles that show more than600m of offset in Neogene deposits(Demyttenaere and Laga,1988)and about150m at the base of the Pliocene(De Batist and Versteeg, 1999).By considering the offset of the main terrace of the Mass River determined by Paulissen et al.(1985),Camelbeeck and Meghraoui(1998)obtain0.08±0.04mm/year for the average Late Pleistocene vertical deformation along the Feldbiss fault. Near the town of Bree(Figures1and2)and along the Feldbiss fault,a prominent northwest–southeast-trending fault scarp separates the Campine plateau to the west from the Roer Valley Graben to the east(Paulissen,1973).The geomorphic expression of the scarp consists of a10-km-long escarpment that has15–20m of vertical topographic relief(Figure2).The Belgian Geological Survey acquired150reflection seismic lines in the region with a dozen crossing the scarp(Demyttenaere, 1989).On different sections,the scarp coincides at the surface with the surface projection of the Feldbiss fault zone and can therefore be considered the morphological expression of the fault’s recent activity.The Bree fault scarp corresponds to the northeastern border of the Campine Plateau(Figure2),which is covered by terrace gravels deposited by the Mass River(Zutendaal gravels)during the Cromerian(between770000and350000years BP)and which overly sands of Upper Miocene age(Diest Formation)(Paulissen et al.,1985).In the downthrown block (Roer Graben),the Zutendaal gravels have been eroded by the Rhine and Maas Rivers,which afterward deposited the Bocholt sands(Paulissen,1983).These formations constitute the basement on which the Maas formed its different terraces at the end of the Middle Pleistocene and during the Late Pleistocene.These terraces are the typical landscape of the region.The region was later covered with aeolian sands during the Saalian and Weichselian glacial ages,which were mixed with the other near-slope deposits in the vicinity of the fault scarp.Afinal phase of deposition created the Holocene alluvium in the center of the Maas Valley.The lithology logs of two boreholes(Van der Sluys,1997)drilled on each side of the scarp are given in Figure3.On the Campine plateau(hole H1),the Zutendaal gravels directly overlie the Upper Miocene sands of the Diest Formation,which were encountered at 11m depth.In the Roer Graben(hole H2),the thickness of the Middle Pleistocene river terraces reaches40m,while the top of the Diest Formation was found at233m depth,belowF IG.1.Quaternary faults and seismic activity in the lower Rhine embayment.The Bree fault scarp is located along the Feldbiss fault southeast of the town of Bree.80Demanet et al.a succession of sand and clay layers from Lower Pliocene to Upper Pliocene.The depth difference in stratigraphic horizons between the two boreholes gives strong evidence of tectonic activity along the Feldbiss fault zone.Multiple scarplets are superposed on the overall fault scarp,and the frontal fault trace consists of an en echelon geom-etry that suggests a component of left-lateral slip.The fault dips 70◦northeast and offsets young deposits (mainly late Weichselian aeolian cover sands and local alluvial terraces).Leveling profiles across the frontal fault scarp yield a vertical displacement ranging from 0.5to 3m.A three-year detailed paleoseismic investigation (1996–1998)shows that this frontal scarp corresponds to the latest coseismic (occurring during an earthquake)surface ruptures along this segment of the Feld-biss fault.These studies (Camelbeeck and Meghraoui,1996,1998)suggest that the most recent large earthquake occurred along the fault scarp between 610and 890A.D.and produced a vertical coseismic displacement of 0.5to 1.0m,with a mini-mum moment magnitude estimated as 6.3M W .Paleoseismic in-formation combining the trench and geomorphic observations suggests the occurrence of two surface-faulting earthquakes during the last 20000years.A third dates between 28000and 42000years BP .DATA ACQUISITIONFigure 2shows the location of the four sites where geophysical profiles were performed perpendicular to the fault strike.At these sites trenches were later excavated for a paleo-seismic study (Meghraoui et al.,2000).Six geophysical methods were applied across the scarp:(1)electrical profiling,(2)EM profiling,(3)electrical tomography,(4)GPR,(5)seismicF IG .2.Location and geological map showing the frontal escarpment of the Feldbiss fault near Bree and the studied sites (labeled 1to 4).The seismic line (SL)is located between sites 1and 2,at a right angle to the scarp.H1and H2are the boreholes described in Figure 3.Contours indicatetopography.F IG .3.Stratigraphic logs of boreholes H1and H2along a schematic southwest–northeast cross-section (after Van der Sluys,1997).Imaging Active Faults81refraction tests,and(6)high-resolution seismic reflection pro-files(Telford et al.,1990;Reynolds,1997).Geophysical tests were performed along the axis of each planned trench except for the seismic reflection profile,which was carried out between sites1and2(Figure2).As afirst step,the variation of the ap-parent ground resistivity along the scarp was measured with electrical and/or EM profiling.EM surveying was conducted with two separate coils connected by a reference cable moved along the profile at discrete intervals with a constant coil spac-ing(Reynolds,1997).The instrument provides a direct reading of the apparent resistivity of the ground.In this study,the mea-surement spacing was5m and the intercoil separation was 10m.With horizontal coils,the maximum contribution to the secondary magneticfield theoretically arises from a depth of around4m.In electrical profiling,a Schlumberger configuration with cur-rent electrodes spaced12m apart(50m for site4)was moved perpendicular to the profile,providing measurements of the apparent resistivity of the ground as a function of distance.An electrical tomography survey was performed using the Lund imaging system(Dahlin,1996)with a Wenner configuration and an electrode spacing of1or2m.The data were processed with the algorithm proposed by Loke and Barker(1996)to ob-tain a resistivity section.According to the profile length,the investigation depth was between5and15m.GPR profiles were also performed at three sites with a120-MHz transmitting an-tenna and at site3with a50-MHz antenna.A static correction was made with a mean velocity of80to90mm/ns determined from scattered events.The penetration depth strongly depends on the ground resistivity(ranging between50and500ohm-m in the Bree area)and was limited to a few meters.The GPR vertical resolution was smaller than0.5m with the120-MHz an-tenna used.At two sites,seismic refraction profiles,44and70m long,were carried out with a geophone spacing of1m and three tofive shots.The source was a hammer,and twenty-four10-Hz geophones were connected to a16-bit seismograph.Finally, one seismic reflection line was run in a northeast–southwest direction perpendicular to the fault scarp(Figure2).The pro-file extends150m with a4-m source interval.A gun provided the source,stackedfive times for each source location.The op-timum window(Hunter et al.,1984)was determined from30to 56m from a walkaway test.Data were recorded with a16-bit seismograph from40-Hz geophones.The stacked data have a maximum of six-fold subsurface coverage.Processing was performed using SU software(Cohen and Stockwell,1998), and the sequence included static corrections,F-Kfiltering, NMO corrections,prestack band-passfiltering,CDP stack and poststack band-passfiltering.RESULTS AND INTERPRETATIONThe results of geophysical tests parallel to trenches T1to T4 are presented in Figure4and Figures6to8as well as a simpli-fied geological description of each trench.The seismic reflec-tion profile is shown in Figure5.Site1Thefirst site is located near a stream that cuts a small uplifted alluvial terrace.The trench,which is only2m deep,reveals late Weichselian cover sands,the upper part of which has been reworked by the small river(Figure4a).Disruption of(1)twogravel horizons within the cover sands and(2)the bleachedHolocene soil at the top indicates the near-surface presenceof a normal fault dipping to the northeast and closely aligningwith the frontal escarpment.An overlying soil bed just belowthe plough zone does not appear to be affected.Electrical profiling data clearly delineate the fault at a dis-tance between50and65m(Figure4a)by a sharp increase ofthe apparent resistivity values,from70ohm-m in the south-west block to more than250ohm-m in the northeast block(Figure4b).An accurate location(within a few meters)ofthe fault is,however,impossible to assess.The electrical to-mography section(Figure4c)shows a strong lateral resistivityvariation around50m with a contact dipping to the northeast.In the southwest block,a2-m-thick resistive layer overlies aconductive formation,while the northeast block consists onlyof the resistive layer.Here,the fault juxtaposing different soillayers can be located at the surface with an accuracy<2m.A second strong lateral resistivity variation at20m could beinterpreted as a fault dipping to the southwest.However,thiswas shown neither on the seismic profile nor in the trench,andthe anomaly probably results from a sedimentary variation.A70-m-long seismic refraction profile was performed acrossthe scarp.The time–distance graph inferred from the refractedwave analysis for the direct shot(Figure4b)shows an unusualdecrease of the apparent velocity from1690to720m/s in thesubsurface.This crossover point is located around50m andfits perfectly with the position of the fault.The interpretationof the seismic data(Figure4a)with the generalized recipro-cal method(Palmer,1981)shows that the conductive underly-ing layer is characterized by a relatively high seismic velocity(V p=1400m/s).In the southwest part of the section,this hori-zon is covered by a thin layer with a velocity of470m/s,whichdramatically increases in depth across the fault to reach4m inthe hanging wall.The limit between the two seismic horizonscould correspond to the depth of the water table,which wasless than2m in the footwall.Both geophysical methods clearlyindicate the presence of a fault below the topographic scarp,juxtaposing two blocks with different resistivity and seismicvelocity values.The corresponding GPR section is presentedin Figure4d,where thefirst30ns corresponding to the directwave have been muted.The maximum penetration depth isabout4m,corresponding to a two-way traveltime of100ns.In the southwest part,the section reveals two main horizontalreflectors(R1and R2),which are clearlyflexured and cut bytwo fault branches.The main one(F1)is located at about50malong the profile,whereas the second fault branch F2prob-ably does not extend to within the reach of the trench.Theshallower reflector(R1)is located at1.6m depth(40ns)andcorrelates with the lower gravel horizon exposed at the bottomof trench1.The northeast part of the section is characterized bya wedge shape with a southwest-dipping strong reflector(R3)at its base.The base of the wedge is located at3.2m depth.Thedifferent layers inside the wedge appear to beflexured in thevicinity of the fault.Seismic line SL(Figure5),150m long,trends southwest–northeast and crosses the frontal escarpment(F)at a rightangle.In the Roer graben(northeastern block),the seismicsection reveals several well-defined reflections down to0.2s.These seismic horizons are cut at105m by a fault(F)whose82Demanet et al.F IG.4.Site1.(a)Schematic stratigraphic cross-section and seismic velocity model.(b)Electrical profiling(EP)and seismictraveltime curves(SP).(c)Electrical tomography.(d)Radar section(120MHz).Imaging Active Faults 83location aligns well with the one delineated near the surface by the trench and shallow geophysical data.Displacement on this fault can be traced down to 150m.In the southwestern block,the penetration depth is lower and the reflections are less coherent.The bending and the disturbance of these reflec-tors,however,suggest the presence of two other faults at 45and 58m along the profile (Figure 5).In the Roer Graben,the borehole data (Figure 3)and the seismic stratigraphy study of De Batist and Versteeg (1999)allow us to correlate prominent reflections with stratigraphic unconformities.The three main seismic horizons are at 40,110,and 200ms,corresponding to depth values of 30,82.5,and 150m with a seismic velocity of 1500m/s (Figure 5).The two deeper reflectors could coincide with the interface between the Mol sands and the underlying Brunssum I clay layer and with the top of the Miocene (formation of Diest),respectively.The shallower seismic horizon (30m)could correspond to the bottom of the Middle Pleistocene terrace deposits,which was found at 37m in borehole H2.However,borehole H2is situated within the graben at a greater distance from the border fault.In the footwall,the Middle Pleistocene river terraces are only about 11m thick and directly overlie the Late Miocene Diest sands,precluding the existence of correlative seismic reflectors on both sides of the fault.Site 2The second site is located a few hundred meters away from site 1but on a much steeper portion of the Bree fault escarpment.The trench at this site (Figure 6a)was between 2.5and 3.5m deep and exposed Middle Pleistocene coarse gravel deposits with intercalated lenses of clayey sand on the upper portion of the slope.The stratigraphy of the lower slopeis F IG .5.Seismic profile across the Bree scarp near site 1with the surface topography.totally different,consisting of finer grained cover sands and re-worked cover sands of Late Pleistocene (mainly Weichselian)age.From bottom to top the following succession is observed:reworked gravelly cover sands;a 20-cm-thick bed of clayey sand;finely laminated cover sands;a complex unit of grav-elly and silty sand containing an irregular,discontinuous clay level at its base;a bleached unit of silty sand;and finally the plough zone.The laminated sands and the overlying unit ex-hibit channel-like thickness variations.The upper and lower slopes are separated by a zone of two normal surface faults,dipping to the northeast and associated with a complex se-ries of colluvial gravels,sands,and silts produced by fault scarp degradation following surface rupture (Meghraoui et al.,2000).The presence of the fault is clearly shown on all the geo-physical results.The resistivity values obtained by EM and electrical profiling (Figure 6b)exhibit a sharp increase at the approximate emplacement of the fault,from 80ohm-m to the southwest to more than 140ohm-m in the northeast block.The resistivity increase is slightly shifted with regard to the fault trace,probably as a result of the fault dip.The time–distance graph inferred from the refracted wave analysis (Figure 6b)and the velocity model (Figure 6a)show a similar evolution with a dramatic lateral variation of the apparent velocity values from 1840to 710m/s in the layers below the plough zone.These sediment property contrasts primarily reflect the difference of water table level on both sides of the fault,with the fault acting like a hydrological barrier.In the footwall,the shallow water table limited the trench to a depth of 2to 2.5m.In the hanging wall,groundwater was not encountered down to at least 4.5m.A farm well located near the top of the slope indicates that this situation persists.Thus,the saturated footwall sediments are characterized by lower resistivity and higher seismic velocity84Demanet et al.F IG.6.Site2.(a)Schematic trench cross-section and seismic velocity model.(b)Electrical profiling(EP),electromagnetic profiling(EM),and seismic traveltime curves(SP).(c)Electrical tomography.(d)Radar section(120MHz).Imaging Active Faults85values.A2-D image of the fault zone was obtained by the elec-trical tomography method.Data processing(Figure6c)clearly indicated the fault position by a lateral resistivity variation at a distance of around20m.The fault-controlled groundwater level in the hanging wall is clearly shown on the tomographic section by a resistivity decrease at depth,resulting from the presence of saturated sand.In the vicinity of the fault,the wa-ter table depth in the hanging wall is estimated to be around 6m.On the northeastern side,the electrical section presents a more complex pattern,with low-resistivity values close to the surface.This may be related to the presence of irregular clay patches at the base of the channel-like structures described above.The last technique used in this study is GPR.The radar sec-tion is presented in Figure6d.A static correction has been applied with a mean velocity of90mm/ns.In the southwestern part of the section(0–20m),a few irregular reflections clearly appear between20and80ns(0.9and3.6m deep).The strong gully-shaped reflector may well correspond to afluvial chan-nel within the Zutendaal gravels,below the reach of the trench. Around20m,the reflections are dipping northeastward toward the fault zone,probably as a result of fault movementflexur-ing.At that distance,one can also observe a variation of the penetration depth between the northeastern and southwestern parts of the section.This location corresponds to the fault trace mapped in the trench,and the perturbations in the reflections fit with the structures observed in the exposed coarse gravel layers.In the northeast,the radar data show a succession of domes and troughs whose positions correspond to the series of channel-like features in the laminated cover sands and in the overlying unit.Apparently,these features do not correspond to realfluvial channels,but they are interpreted asflow folds in-duced by liquefaction and subsequent failure of the laminated sand unit,which may have been triggered by a paleoearthquake (Vanneste et al.,1999).Site3Site3is located about1.5km southeast of site1on theflank of a small river valley crossing the scarp.The frontal escarpment runs along the top of the hill,and the southwest–northeast-trending excavation has pointed out two major branches of normal faulting extending to just below the plough zone in the southwestern part(between65and72m)and a buried fault at about105m in the northeastern section(Figure7a).The west-ern fault zone exhibits major displacement,as it juxtaposes Middle Pleistocene(Zutendaal gravels)to Late Pleistocene sandy deposit;the eastern buried fault displaces these latter sediments only about1m(Meghraoui et al.,2000).EM pro-filing(Figure7b)estimated the approximate location of the fault zone by an increase of apparent resistivity values from the southwest block(about95ohm-m)to the northeast block (125ohm-m).This fault zone was better delineated by the elec-trical tomography(Figure7c)between70and75m along the profile.Contrary to site1,the dip of the fault was not clearly de-termined from the electrical section,which mainly shows a low-resistivity zone dipping to the southwest.The buried fault does not appear clearly on the tomography section and on the EM profile,suggesting that its throw is not very important at shallow depth.A GPR profile was performed50m to the southeast of the trench to avoid diffracted events generated by the presence of trees.In this area,the maximum penetration depth is about 6m,with an antenna of50MHz.The southwest fault zone is clearly shown by the fault-related structures and the termina-tion of reflectors,while the buried fault is again poorly indica-ted.On the other hand,20m to the south of the main fault zone an additional fault branch appears which could be the second major branch of the fault zone observed in the adjacent trench. Site4Site4is located5km to the southeast of site1(Figure2).In this area,the frontal escarpment occupies the lower part of the slope.The3.5-m-deep trench with a stratigraphic cross-section is given in Figure8a.It exposed coarse,clayey and gravelly Maas River sediments corresponding to the Zutendaal grav-els in the footwall,juxtaposed by a narrow fault zone to more fine-grained,partly reworked cover sands with some gravel horizons in the downthrown block.Two wedges of reworked Maas material are present in the hanging wall close to the fault, wedging out downslope,whereas the main Maas River terrace is probably downthrown beneath the trench bottom.The di-rectly observable fault displacement is,however,limited to about60cm,based on the offset of the base of the laminated cover sands in Figure8a.Electrical and EM profiles(Figure8b)performed with dif-ferent spacing values,and hence different penetration depths, show a general decrease of resistivity across the fault zone with-out a strong gradient displaying the fault location.Below a shallow and irregular resistive layer,the upper7m on the elec-trical tomography section(Figure8c)are mainly characterized by a relatively uniform resistivity ranging between100and 200ohm-m with a disturbance around60m.Somewhat deeper, the section shows a lateral resistivity gradient across the fault and an asymmetrical synclinal structure in the downthrown block.The depth of the groundwater table was at least6m in the footwall and more than9m in the hanging wall,as indicated by hand borings.On the radar profile(Figure8d),which has a penetration depth of about4m,the position of the main fault zone is shown by a distinct change in reflectivity and penetration depth be-tween footwall and hanging walls:the footwall is characterized by discontinuous,incoherent reflectors and small penetration depth,most probably resulting from the high clay content of the strongly altered Maas deposits.Some isolated reflectors,e.g., the dipping segment between35and45m,may correspond to the gravel-rich base of erosional channels,several of which have been identified on the trench wall.The hanging wall,on the other hand,shows more regular reflectors extending over a larger depth interval.The stratification of the hanging-wall sediments is mostly parallel to the surface slope.At the base of the hill slope,the strata show a counterslope tilt because of thrusting along several detachment planes.This deforma-tion structure clearly appears on the radar section as a set of disrupted reflectors with associated diffractions.The general hanging-wall structure of an asymmetrical synform appearing on both the radar and the electrical tomography profiles indi-cates that deeper hanging-wall layers are slightly dipping to-ward the main fault.This has been confirmed by hand bor-ings extending5m below the trench bottom.In particular,the strong reflector in the lower part of the radar section can be correlated to a30-to40-cm-thick clay bed dipping from the far。
《建筑结构抗震设计》总复习（武汉理工配套）考试的具体题型和形式可能会有变化，但知识点应该均在以下内容中。
复习不要死记硬背，而应侧重理解.第一章：绪论1.什么是地震动和近场地震动？P3由地震波传播所引发的地面振动，叫地震动。
其中,在震中区附近的地震动称为近场地震动.2。
什么是地震动的三要素？P3地震动的峰值（振幅)、频谱和持续时间称作地震动的三要素。
3. 地震按其成因分为哪几类？其中影响最大的是那一类？答：地震按其成因可分为构造地震、火山地震、陷落地震和诱发地震等几类，其中影响最大的是构造地震。
4。
什么是构造地震、震源、震中、震中距、震源深度？P1 答:由于地壳构造运动使深部岩石的应变超过容许值,岩层发生断裂、错动而引起的地面震动，这种地震称为构造地震，一般简称地震.地壳深处发生岩层断裂、错动的地方称为震源。
震源至地面的距离称为震源深度。
一般震源深度小于60km的地震称为浅源地震；60～300km的称为中源地震；大于300km的称为深源地震；我国绝大部分发生的地震属于浅源地震,一般深度为5~40km。
震源正上方的地面称为震中，震中邻近地区称为震中区，地面上某点至震中的距离称为震中距。
5。
地震波分哪几类?各引起地面什么方向的振动？P1—3 答：地震波按其在地壳传播的位置不同可分为体波和面波。
在地球内部传播的波称为体波，体波又分为纵波（P波）和横波（S波）。
纵波引起地面垂直方向的震动，横波引起地面水平方向震动。
在地球表面传播的波称为面波.地震曲线图中，纵波首先到达，横波次之，面波最后到达.分析纵波和横波到达的时间差，可以确定震源的深度。
6。
什么是震级和地震烈度？几级以上是破坏性地震？我国地震烈度表分多少度？P4答：震级：指一次地震释放能量大小的等级，是地震本身大小的尺度。
（1）m=2～4的地震为有感地震.(2)m〉5的地震，对建筑物有不同程度的破坏。
(3）m>7的地震，称为强烈地震或大地震。
地震烈度：是指某一区域内的地表和各类建筑物遭受一次地震影响的平均强弱程度。
