1-D N umerical S imulation for Comprehensive G ophysical e P rospecting of S eismic R fraction e and H h igdensity R sistivity e

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1 International Conference on Mechatronic, Electronic, Indutrial and Control Engineering (MEIC 04) -D N umerical S imulation for Comprehenive G ophyical e P ropecting of S eimic R fraction e and H h igdenity R itivity e Xi Jianjun Hebei Electric Power Deign &Reearch Intitute, Hebei Shijiazhuang, 05003,China @qq.com Zeng Zhaofa Wang Zhejiang Chen Xiong Huangling Abtract Comprehenive geophyical propecting ha been widely ued but the theoretical evidence ha not been clear by mot reearcher. The paper how out a one dimenion eimic refraction imulation by ray-trace technology under a one dimenion horizontal geo-model. And then uing digital filter method and electrical ounding and interpretation to complete high denity reitivity imulation with variable electrode pace. Both reult are compared by each other, and the reearch reult how that both eimic and electronic method could couple with the geological model very well and the both can be mutually verified, o it improve the interpretation correctne. Thi work give the theorie bae for comprehenive geophyical propecting technology with eimic and electrometric method and got ome meaningful concluion. Keyword-Comprehenive geophyical propecting; eimic refraction method; high denity reitivity method; Numerical modeling of the pro and con I. INTRODUCTION Seimic refraction i an engineering geophyical propecting method, which determine the velocity in refraction interface and the embedded depth of foundation. However, High-denity reitivity method i one of electric propecting to predict the ditribution rule of geological ma from electric property difference in the ground. Both the two and their comprehenive methodology are widely ued in engineering invetigation [~4]. The comprehenive method i more often applied for engineering detection in China. It i commonly thought that comprehenive invetigation method can reduce uncertaintie, but few reearcher focu on the theoretical bai of comprehenive geophyical method [5, 6]. The article ha done a numerical imulation repectively on the two detection method regarding a geological model in a horizontal level. The reult how that high-denity reitivity method can be ynergitically applied with eimic refraction method. The thickne of weathered layer under the two method dovetailed nicely, which further provide a theoretical bai for comprehenive geophyical method [7~9]. II. METHODOLOGY When wave travel through the underground medium and meet an interface, reflection, refraction and tranmiion take place. If the wave velocity above the interface i maller than that below the interface, the eimic ignal refract ignificantly [0]. Seimic refraction i to invetigate the geological information through the initial value of hallow refractive wave. It cover the artificial excitation of eimic wave, and the relation between the arrival time of refractive wave on the ground to the local ditance from the excitation point [, 3]. High-denity reitivity method i a propecting technique by integrating electrical profiling and meaurement. The reitivity method can get high-denity ample, have imaging propertie on two-dimenional geo-electric cro ection, alo intuitively reflect the medium change of different underground propertie, and alo how the depth and characteritic of anomalou bodie [, ~]. Therefore, it hould be atified for comprehenive invetigation method that there i difference in flexibility and electricity for refractive wave when the target and urrounding ground i invetigated. 04. The author - Publihed by Atlanti Pre 370

2 Figure. One horizontal layered geo-model A indicated in Fig., there are two horizontal layer below the ground urface. The reitivitie on each level are 50gm and gm repectively. The wave peed i 000 m/ and 3000 m/. The thickne i 0 m and infinity. The electric current i I. A. Direct calculation ) one-dimenion direct imulation Directive wave i an earthquake wave that tranmitted directly from the hypocenter to each acceptance point at a peed of v without any reflection or refraction. When the hypocenter lie near the ground urface and the obervation i along the longitudinal meauring line, the time plot equation [3] i: t x / v () Furthermore, if it i a ingle leveled refractive layer, the time plot equation of refractive wave i: x v t v v v h co( in a ) () If the reflective interface i parallel to the ground urface, the time plot equation for reflective wave i: t g 4h x v (3) Applying Eq. () ~ (3), numerical imulation i performed when h = 0 m, Vp = 000 m/, Vp = 3000 m/. The imulation curve for directive wave, refractive wave and reflective wave and time plot curve can be obtained finally, which i indicated in Fig. and Fig.3. Figure. Numerical imulation for eimic direct wave, reflective wave and refractive wave in a i--ngle horizontal geo-model Figure 3. Time plot curve for direct wave, one-horizontal layered refractive wave and reflective wave ) The direct imulation for -D model explored by high denity reitivity method From the equation in the journal [5] (-05 ~ -09), the electric potential for point-ource electric current on the ground urface (Z = 0) can be derived a: I U( r,0) B( m) J 0 0( mr) dm The expreion for ymmetrical quaternary depth finder ( MN 0 ) i: ( ) 0 ( ) ( ) (4) r r T m J mr mdm (5) where T( m) i reitivity tranfer function, ( ) B( m), and Bm ( ) i kernel function. T m In Eq. (5), the reitivity tranfer function can be derived from digital filtering method, which i: ( ) ( ) ( ) i T kx ix a k i x (6) In Eq. (6), in i called a( k i) x x J ( k i) x d x filter factor. x y If r e, m e and T ( y) T ( e y ) and x ( x) ( e ) the reitivity i changed to a faltung form: ( x) T ( y) b( xy) dy xy ( xy ) b( xy) J ( e ) e and dicrete ampling i done, Equation (5) can be derived into another form: L ( i) T( k) b( i k) ik l where the filter factor in i y ( ik ) y. b( i k) J ( i k) y e d y (7) when 50g m, 300g m, h 0m h () i,, can be obtained uing digital filtering method. Moreover, T(y) can be calculated. Finally the 37

3 theoretical curve can be obtained uing digital filtering. The apparent reitivity curve i hown in Fig.4. The imaging i performed uing Redinv oftware and finally the direct imulation curve i found in Fig.5. Figure 4. The apparent reitivitie curve under the ingle-layered geomodel via high denity reitivity method. Figure 5. The direct imulation curve under the ingle-layered geo-model via high denity reitivity method. B. The data interpretation and inverion modeling There are many data interpretation method for eimic refraction, uch a geo-metrograph by Hagedoom, Hale diagram, delay time method, interception-time method, Palmer generalized exchange method. The article adopt the t0 method in the meeting obervation ytem and make the data interpretation to the refractive wave in Fig., and thu h = 9.8 m. In addition, a oberved in Fig.5, h = 9.3 m. The thickne for weathered layered are conitent to h = 0 in thi model. III. RESULT AND ANALYSIS The invetigation zone lie in the Ji an ection, Xia Lin Line that i frontier defene road. The project i to make a geological propection on in-line tunnel contruction. The ground in thi area i mainly compoed of ignimbrite and overlying quaternary ytem. The higher the weathering level i for ignimbrite, the larger the thickne of covering layer change in a lateral direction. The buried depth of bedrock uually range from 8 to 35 meter, and the velocity of longitudinal wave i around 500~3900 m/; the velocity of longitudinal wave in the upertratum change from 500 to 800 m/. A a reult, a velocity interface i well-defined between the bedrock to upertratum, which erve a prerequiite for detecting buried depth in the bedrock a well a tructural configuration in eimic refraction. The reitivity of bedrock layer i relatively low, for which apparent value i uually 40~500Ω m. The quaternary ytem i mainly ditributed in ome cleuch and foot lope, which i characterized a a looely compoed tructure of graveled loam and loam andy clay. The reitivity change very ignificantly. The detection ha adopted NZ4 hallow layer eimograph. An exploive i elected a eimic in the exciting point of the hypocenter. Beide, a 38 Hz dicriminator i applied a ytem to trace and detect wave ignal. By making comparion in field invetigation, the working parameter are: Maximum track pitch 0m, offet 5m, record length 04 m, ample rate 0.5m. Fig.6 illutrate the original eimic wave form collected under the working parameter. Moreover, eimic refraction proceing oftware i adopted to proce the original recorded data and obtain a group of initial value; the time graph for refractive wave i obtained by Grapher. The graph can be further interpreted uing t0 method. Finally, the velocity and depth profile for refractive layer can be drawn by Auto Cad, a een in Fig.7. 37

4 (a)hot locat at the trumpet from the eat of the line (b)hot locat at the large ize from the wet of the line Figure 6. The original record chart of eimic refractive wave Figure 7. The reulting figure about the peed and depth of eimic refraction layer Figure 8. The forward chart of high-denity reitivity method Figure 9. The inverion chart of high-denity reitivity method However, high-denity reitivity method will apply Jiao Peng E60D electrical intrument. The winner operation i elected with 0-meter electrode pacing. After reitivity value under different electrode pacing i collected, data proceing i performed by Redinv to get the inverion chart, a illutrated in Fig.8 and Fig.9. It i found from eimic refractive chart (Fig.7) that, the buried depth of covering layer from eat 70 meter i h =5.m. However thi value i 5.5m for high-denity reitivity chart in Fig.9 The two chart are approximately the ame with minimal error. Moreover, both two chart how a gradual increaing buried depth from eat to wet. IV. CONCLUSION The theoretical bai for comprehenive invetigation method i et by one-dimenional data imulation uing eimic refraction and high-denity reitivity technique. The hallow eimic refraction i baed on the poitive difference in wave velocity between 373

5 bedrock and upertratum. High-denity Reitivity method i baed on the difference in electrical propertie between target and wall rock. Hence both hould be atified for comprehenive invetigation technique. It i alo found that refractive method can delineate the bedrock interface with high propecting preciion but only reflect the urrounding area of bedrock urface. A for high-denity reitivity method, it can determine the change in electrical propertie of the rock in different underground depth, but the preciion i very low. Therefore, thee two method can ynergitically work with complementary advantage. REFERENCES [] Di Qinyuan, Wang Miaoyue, Yan Shoumin, et al. The application of the high denity reitivity method for the ea wave-proof dam in ZHUHAI-HARBOUR. Progre in geophyic, Vol., No., 79-88, 997. [] Ge Shuangcheng, Li Xiaoping, Shao Chenchen, et al. Application of eimic refraction and reitivity for exploration of reevoir dam ite. Progre in geophyic, Vol. 3, No. 4, , 008. [3] Lei Wang, Xiao Hongyue, Den Yiqian, et al. Engineering and environmental geophyical tutorial. Beijing:Geological publihing Houe, 45-34, 006. [4] Liu Guoxing, principle and method of electrical propecting. Beijing:Geological publihing Houe, 49-74, 005. [5] Li Jingming. Geoelectric field and electrical propecting. Beijing:Geological publihing Houe, 74-5, 007. [6] Lan Xing, Zhang Wei. The Application of Shallow Seimic Reflection and High Denity Reitivity Method to the Exploration in Hanwang Area. Chinee journal of engineering geophyic. 0,, 9(6), [7] Zhao guanghui. High denity electronic propecting and it application. Mineral reource and geology. 006,4,0(): [8] Zhou Zhuheng, Jiang Chanjun, Guo Yougang. Application of Shallow Seimic Reflected Wave Method to Tunnel Engineering Invetigation. Invetigation of cience and technology 008, 6:6-64 [9] Wei Xing, Wang Yanbin, Chen Xiaofei. Hybrid PSM/FDM method for eimic wavefield imulation. Acta eimologica in ica. 00, 07, 3(4): [0] Jiang Wei. Application of Finite Elemen Numerieal Simulation TO Shallow Seimie propecting. Mater degree thei, The intitute of geophyic of china earthquak adminitration, 0 [] Yan Jia-yong,Meng Gui-xiang,Lv Qing-tian, et al. The progre and propect of the electrical reitivity imaging urvey. Geophyical & geochemical exploration. 0, 08, 36(4): [] Guo Qinghi. The numerical imulation reearch of high-denity electrical method in kart cave exploration. Mater degree thei, Southwet jiaotong univerity,