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					    A 3D Geological Modeling and Numerical Simulations

                        of Near-fault Endangered Field


              Haiying Cheng1, Huagang Shao1, Hualin Wang2, Hongwei Wang2

     1
         Department of Computer Science and Information Engineering, Shanghai Institute of
                               Technology, Shanghai 200235, PRC
                                 {chenghaiying, hgshao}@sit.edu.cn
              2
                  Earthquake Administration of Shandong Province, Jinan 200072, PRC
                              david1978@126.com, hong2006@163.com



         ABSTRACT:         It is very important to study the Near-fault endangered field for
         earthquake engineering, earthquake forecasting and reducing earthquake
         disaster. This paper is based on the correlative data and geology information of
         moderate and upwards earthquakes of Zibo City, Shandong, China. A 3D
         geology model of the main active fault of Zibo City (Zhangdian-Renhe Fault) is
         created. Numerical simulations of the near-fault disservice field have been
         performed, and numerical results are discussed with comparing the
         experiments.

         Keyword: fracture; earthquake; near-fault; numerical simulation

1   INTRODUCTION

Near-fault ground motion has been an active research field of Seismology and
Earthquake Engineering in the recent ten years. In the 80th of 20 century, strong
ground motion records were accumulated very much faster than before, especially
during the Loma Prieta (1989, Ms=7.1), Northridge (1994, Ms=6.7), Kobe (1995,
Ms=6.9) and Jiji (1999, Ms=7.3) earthquakes, there were tens or more than hundred
pieces of accelerogram recorded in each event. Some significant engineering
characteristics, such as near-fault rupture directivity effect, hanging wall effect,
crystals wave guide effect and basin edge effect, were recognized from the
recordings.
    In many areas of the world, the threat to human activities from earthquakes is
sufficient to require their careful consideration in the design of structures and
facilities. So it is very important to study the Near-fault Endangered Field for
earthquake engineering, earthquake forecasting and reducing earthquake disaster. The
goal of earthquake-resistant design is to produce a structure or facility that can
withstand a certain level of shaking without excessive damage. In urban active fault
surveying project,research on the spatial data modeling based on earthquake geology
and active tectonics is very important for interrelated application fields. In this paper,
Explicit Lagrangian finite difference method is adopted to numerically reveal the
characteristics of distortion field, stress field and displacement field of near-fault zone.
The results can show the characteristics of mutual contact blocks’ deformation, and
because of the stiffness puzzling equation in the computer easy to achieve, calculation
is fast and taking up small storage space.



2    GENERAL SITUATION OF THE PROJECT

Zibo City is a developer region in economy and culture of Shandong province. It
locates at the important geotectonic situation, spans the East Hebei-Bosea fault zone,
West Shandong fault zone and East Shandong fault zone, and lies in the combined
part of uplift and depression. There are three main faults in Zibo City which are
Zhangdian-Renhe fault, Wangmu Mountain fault and Wangmu Mountain offset fault.
This paper mainly simulates the geologic condition of Zhangdian-Renhe fault.
Zhangdian-Renhe fault is about 50 kilometers long, spread from south to north. The
characteristic of faultage structure surface, the scrape on the faultage surface and the
quartz chipping structure surface indicate that the rupture way is glue rupture mainly,
and creep rupture partly.



3    MODEL DESIGNING AND RESULTS DISCUSSION

There are five experiment segments considered along the Zhangdian-Renhe fault. The
location of the concealed fault, the burying depth of superior breakpoint and the
delamination of medium are chosen according to the data provided by Earthquake
Engineering Academe of Shandong Province. The choice of the experiment segments
is based on the consideration of the influence of the concealed rupture to Zibo city
zone.
   In this paper we chose the results of the second segment as the examples to
illuminate the simulation to Zhangdian-Renhe fault. The second segment has four
layers, which are cultivated soil (cover layer), clay, weathered bedrock and integrated
bedrock that are from the earth’s surface down.
   The inclination of the computing model is 45 degree, and there is 5 meters
dislocation between the lower block and the upper block. The topside is cover layer.
There are 100 meters to the left of the interface of the fault and 200 meters to the right,
120 meters thick of Z-direction and 1000 meters long of Y-direction.
   The generated model has 83500 calculation elements and 105084 grid points. The
interval between the grid points near interface is 5 meters, and the interval between
the grid points far interface is 10 meters.




                                        Fig.1   Group




                                Fig.2 Location of the interface
  Here, the extracted figures are the group figure and the interface figure. The group
figure is also called appearance figure, which is shown in Fig.1. The interface figure
can indicate the location, incline and obliquity of the interface, which is shown in
Fig.2.
  After completely computing with the seismic wave (Ms=5.5) inputted, it outcomes
the displacement contour of profile, which is shown in Fig.3, the displacement
              of section plane in level direction, which is shown in Fig.4, and the
distributing Frame 001  05 Jun 2007  Flac3d Mesh to Tecplot Version 10
                                                                                                                                                        Z
displacement distributing of section plane in uprightness direction, which is shown in
Fig.5.                                                                                                                                                  Y     X




                                                                                                                          3
                                                                                             0.005                 53 7
                                                                                                            0 10                -0.005
                                                                                                     -0.0                                -0.01

            100                                                                                                                         -0.015
                                                                                                                                    -0.02
                                                                  -0.0
                                                                         00
                                                                              10
                                                                                   79
                                                                                        92




                                                        -0.000107992
           Z




                                                                                                                                    -0.000107992
               50                                   -0.00105373



                                               -0.005                                                                               -0.00105373




                                         1
                                 -0.0
                0
                                                                                                                                                                  1
                                                                                                                                                                  50
                    0                            50                           100                                   150       200                 250       300        Y
                                                                                                                      X

                                                   Fig.3 Displacement contour of profile


                                              8.00E-03
                                              6.00E-03
                        Displacement/m




                                              4.00E-03

                                              2.00E-03
                                              0.00E+00
                                                    0.00E+ 1.00E+ 2.00E+ 3.00E+ 4.00E+
                                             -2.00E-03
                                                       00    02     02     02     02
                                             -4.00E-03



                Fig.4 Displacement distributing of section plane in level direction

  We consider a consult line 300 meters long along the section plane of the rupture,
compute the displacement of the consult points in X-direction, Y-direction and
Z-direction. The difference between arbitrary two adjacent points’ displacements is
actually the distortion arisen between the two points on the earth’s surface after the
sudden displacement of the lie concealed earthquake fault happened.


                                      1.50E-02

                                      1.00E-02
                    Displacement/m




                                      5.00E-03

                                      0.00E+00
                                             0.00E 1.00E 2.00E 3.00E 4.00E
                                     -5.00E-03+00   +02   +02   +02   +02

                                     -1.00E-02



            Fig.5 Displacement distributing of section plane in uprightness direction

  There are several characteristics of the final computing result.
  (1) When the Ms is changeless, the model of 45 degree inclination and the model
of 80 degree have different result. The displacement distributions in horizontal
direction and in vertical direction of the 80 degree inclination model are 1 magnitude
bigger than the 45 degree inclination model’s. From the results of the numerical
simulation, we can see that the earthquake destroy of the 80 degree inclination model
is worse than the 45 degree inclination model’s at the same earthquake conditions.
  (2) As a specific model, its displacement distribution in vertical direction is more
obvious than that in horizontal direction.
  (3) At the same earthquake conditions, the results of different segments have more
or less difference. Especially the first segment is more different from the other
segments. Its displacement distributions in horizontal direction and in vertical
direction are both tiny. Because the first segment has different geologic conditions
from the other segments, its computing model is elastic, and it has two layers
(weathered bedrock layer and integrated bedrock layer). Whereas the other segments
all have cover layer and diversified soil layers, and Mohr-Coulomb model is adopted
as their computing model.
    (4) In view of the displacement distribution in vertical direction, the most
deformation of the earth’s surface does not appear at the projection of the fault’s
breakpoint on the surface, whereas appears at the scope of 10-100 meters from upper
block.
4     CONCLUSIONS

     (1) Explicit Lagrangian finite difference method can do well in the simulation of
active faults and near-fault endangered field, and Mohr-Coulomb model can
commendably reflect the properties of soil.
     (2) It is needed to do more in 3-D seismic structural model. The rationality of the
model directly constrains and affects the computing result, and any parameter
changed, the results will change. Therefore, the prediction of the deformation of the
earthquake zone is a very complex work, which needs different professional
researchers to cooperate closely.
     (3) The calculated results of this paper can provide guidance and reference for
earthquake prevention, disaster reduction and engineering design.



ACKNOWLEDGEMENTS

The work described in this paper was supported by the key project of Shanghai
Institute of Technology (KJ2009-14) and the project of Shanghai Education
Committee (YYY08027).



REFERENCES

1.    Itasca Consulting Group, Inc. FLAC (Fast Lagrangian Analysis of Continua) User
     Manuals, Version 5.0, Minneapolis, Minnesota, 2005.5
2.    Toro G, Abrahamson N A, Schneider J F. 1997. Model of strong ground motions from
     earthquakes in Central and Eastern North America: Best estimates and uncertainties [J].
     Seism Res Lett 68(1): 41~57.
3.    Toro G, McGuire R. 1987. An investigation into earthquake ground motion characteristics
     in Eastern North America [J]. Bull Seism Soc Amer, 77(4): 468~489.
4.    Wald D J, Heaton T H, Hudnut K W. 1996. The slip history of the 1994 Northridge,
     California, earthquake determined from strongmotion, teleseismic, GPS, and leveling data
     [J]. Bull Seism Soc Amer, 86(1B): S49~S57.

				
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