1. 1. A Project Report on Mapping of Focal Mechanism of Earthquakes in Indian Region By TAICHENGMONG RAJKUMAR From Department of Applied Geophysics Indian School of Mines, Dhanbad Carried out under Student Programme for Advancement in Research Knowledge (SPARK) at Council of Scientific & Industrial Research CENTRE FOR MATHEMATICAL MODELLING AND COMPUTATIONAL SIMULATION (CSIR-C-MMACS) NAL BELUR CAMPUS, BANGALORE-560037 Under the guidance of Dr. Imtiyaz Ahmed Parvez Principal Scientist, C-MMACS, Belur Campus (NAL), Bangalore-560037 Department of Applied Geophysics Indian School of Mines, Dhanbad-826004
2. 2. Date: CERTIFICATE This is to certify that the project entitled Mapping of Focal Mechanism of Earthquakes in Indian Region submitted by Taichengmong Rajkumar to Indian School of Mines, Dhanbad in partial fulfillment of the requirement for the award of the degree for Int. Master of Science and Technology is a record of bonafide work carried out by him under my supervision and guidance at CSIR CENTRE FOR MATHEMATICAL AND COMOUTER SIMULATION (C-MMACS), NATIONAL AEROSPACE LABORATORIES (NAL), BANGALORE. It is also certified that the project work has not been submitted for any purpose elsewhere, in part or full. Dr. Imtiyaz Ahmed Parvez Signature of the Convenor, SPARK C-MMACS Project Guide CSIR Centre for Mathematical Modelling and Computer Simulation (Council of Scientific & Industrial Research) NAL Belur Campus, Bangalore-560037, India
3. 3. ACKNOWLEDGEMENT I am very grateful to my guide Dr Imtiyaz Ahmed Parvez who helped me a lot during the whole project. He has been very kind to me and shared his knowledge with me. I would also like to thank Dr Anil Kumar, Convenor of SPARK for being so patient to us. I also convey my heartiest thanks to Stella madam for her help and support. I would like to thank Prof. Shalivahan sir, HOD, Department of Applied Geophysics, Indian School of Mines, Dhanbad who has always been a support to us. Also I would like to thank my fellow summer interns for helping me throughout these two months.
4. 4. INTRODUCTION Earthquakes occur on faults. A fault is a thin zone of crushed rock separating blocks of the earth's crust. When an earthquake occurs on one of these faults, the rock on one side of the fault slips with respect to the other. Faults can be centimeters to thousands of kilometers long. The fault surface can be vertical, horizontal, or at some angle to the surface of the earth. Faults can extend deep into the earth and may or may not extend up to the earth's surface. Based on the nature of relative movement along the fault it can be classified into three types: (i) Thrust fault (ii) Normal fault (iii) Strike-slip fault The block above the fault plane is called the hanging wall and that below the fault plane is footwall. Dip is the angle between the horizontal surface and the plane of the fault; hade is compliment of the dip. A standard nomenclature rake has evolved for describing slip direction. The actual motion of the two blocks on either side of the fault plane is defined by a slip vector which can have any orientation on the fault plane. The direction of slip vector is given by the angle of slip or rake (). It is measured in the plane of the fault from the strike direction to the slip vector showing the motion of the hanging wall relative to the footwall. Thrust Fault: A thrust fault is a fault along which the hanging wall (upper side of the fault) has moved up relative to the foot-wall. The thrust is one that dips less than 45 and an
5. 5. over thrust that dips less than 10. In pure thrust-faulting the slip vector is parallel to the dip direction and it is upward, so = 90. Thrust faulting involves crustal shortening and implies compression. Normal Fault: A normal fault is a fault along which hanging wall has moved relatively downward. In pure normal faulting the slip vector is also parallel to the dip direction of the fault plane but it is downward i.e = -90 (270). Normal faulting involves lengthening of the crust and implies tension. There are many possibilities concerning the actual movement; the footwall may remain stationary and the hanging wall goes down; or the hanging wall remains stationary and the footwall goes up, or both blocks move down but the hanging wall moves more than the footwall, or both blocks move up; but the footwall moves more than the hanging wall. Some geologists use the term gravity fault in preference to normal fault. Strike-slip Fault: A strike slip fault is a fault along which displacement has been essentially parallel to the strike of the fault, that is the dip-slip component is less or negligible ( = 0 or 180). For = 0, the hanging wall moves to the right so that the opposite wall, faced by an observer, moves relatively to the left. This is called left-lateral slip or sinistral fault. When = 180, the hanging wall moves to the left and the opposite wall faced by an observer moves relatively to the right. This is right-lateral slip or dextral fault. In general will have a value different than these special cases and the motion is then called oblique slip.
6. 6. FOCAL MECHANISM Seismologists refer to the direction of slip in an earthquake and the orientation of the fault on which it occurs as the focal mechanism. They use information from seismograms to calculate the focal mechanism and typically display it on maps as beach ball symbol. This symbol is the projection on a horizontal plane of the lower
7. 7. half of an imaginary, spherical shell (focal sphere) surrounding the earthquake source (A). A line is scribed when the fault plane intersects the shell. The stress-field orientation at the time of rupture governs the direction of slip on the fault plane, and the beach ball also depicts this stress orientation. In this schematic, the gray quadrants contain the tension axis (T), which reflects the minimum compressive stress direction, and the white quadrants contain the pressure axis (P), which reflects the maximum compressive stress direction. The computed focal mechanisms show only the P and T axes and do not use shading. These focal mechanisms are computed using a method that attempts to find the best fit to the direction of P-first motions observed at each station. For a double-couple source mechanism (or only shear motion on the fault plane), the compression first- motions should lie only in the quadrant containing tension axis, and the dilatation first-motions should lie only in the quadrant containing the pressure axis. However, first-motion observation will frequently be in the wrong quadrant. This occurs because a) the algorithm assigned an incorrect first-motion direction because the signal was not impulsive, b) the earthquake velocity model, and hence, the earthquake location is incorrect, so that the computed position of the first-motion observation on the focal sphere (or ray azimuth and angle of incidence with respect to vertical) is incorrect, or c) the seismometer is mis-wired, so that up is down. The latter explanation is not a common occurrence. For mechanisms computed using only first motion directions, these incorrect first-motion observations may greatly affect the computed focal mechanism parameters. Depending on the distributed and quality of first-motion data, more than one focal mechanism solution may fit the data equally well. For mechanism calculated from first-motion directions as well as some methods that model waveforms, there is an ambiguity in identifying the fault plane on which slip occurred form the orthogonal, mathematically equivalent, auxiliary plane. We illustrate this ambiguity with four examples (B). The block diagrams adjacent to each
8. 8. focal mechanism illustrate the two possible types of fault motion that the focal mechanism could represent. Note that the view angle is 30-degree to the left of and above each diagram. The ambiguity may sometimes be resolved by computing the two fault-plane orientation to the alignment of small earthquakes and aftershocks. The first three examples describe fault motion that is purely horizontal (strike slip) or vertical (normal or reverse). The oblique-reverse mechanism illustrate that slip may also have components of horizontal and vertical motion.
9. 9. Seismic Moment Tensor: The seismic moment tensor M can be written in the form of 3x3 matrix as where each component represents one of the nine possible force couples. A force couple consists of two forces acting together. M12 consists of two forces of magnitude f, separated by a distance d along 2-axis, that act in opposite directions along 1. The magnitude of M12 = fd, which has unit of Nm. In the case of M11, two forces of magnitude f are separated by a distance d along 1-axis, and act in opposite directions along 1 axis. This type of couple is sometimes referred to as vector dipole. There will be no torque in case of M11. The moment tensor can be described in terms of three orthogonal axes: P (for pressure; a compressive axis), T (for tension), N (for null). Fault surface along which the earthquake was generated is 45 degree from the P and T axes, and contain the N axis. For any moment tensor there will be two nodal planes. One nodal plane is perpendicular to other nodal plane and intersects along the N axis. One of the planes is the fault surface and other is called as auxiliary plane.
10. 10. Harvard CMT Solution: The Global Centroid-Moment-Tensor (CMT) Project is overseen by Principal Investigator Gran Ekstrm and Co-Principal Investigator Meredith Nettles at the Lamont-Doherty Earth Observatory (LDEO) of Columbia University. The project was founded by Adam Dziewonski at Harvard University (USA) and operated there as the Harvard CMT Project from 1982-2006, led first by Prof. Dziewonski and later by Prof. Ekstrm. During the summer of 2006, the activities of the CMT Project moved with Prof. Ekstrm to LDEO. This research effort is moving forward under the name "The Global CMT Project". The main dissemination point for information and results from the project is the web site www.globalcmt.org. The CMT project has been continuously funded by the National Science Foundation since its inception, and is currently supported by award EAR-0824694. Focal Mechanism solutions in Indian Region: For focal mechanism solutions, I have used CMT HARVARD catalog. For this I have obtained focal mechanism during 01-01-1976 to 31-05-2015. I have used more than 140 focal mechanism solutions of earthquakes. The corresponding epicentres are located inside a quadrangle from 8 N to 38 N in latitude and 68 E to 98 E in longitude. The magnitude range is chosen from 5.5 to 8. Data for plotting Focal Mechanism: Lon lat depth mrr mtt mpp mrt mrp mtp iexp 88.14 33.00 10 -2.05 -1.74 3.80 -0.62 -3.73 0.98 25 88.4 34.2 89.16 30.69 10 -3.48 -0.82 4.31 -0.12 0.82 0.33 25 89.4 31 89.05 27.42 44 -0.24 -1.83 2.07 1.51 -1.12 -1.26 25 89.4 27 70.99 36.80 228 5.47 -6.20 0.73 1.03 1.30 -0.71 25 69.8 34.5 91.28 34.21 10 -0.04 -0.63 0.66 -0.12 0.20 1.23 25 90.5 33.6 73.48 35.22 10 1.81 -1.57 -0.25 -0.46 0.44 0.71 25 74.2 36.3
11. 11. 82.24 31.71 10 -3.12 0.26 2.86 -1.49 1.10 0.06 25 81.2 33.4 68.71 36.20 12 5.16 -1.02 -4.14 -1.21 1.27 -1.73 25 68.8 37.4 93.39 12.99 73 1.02 -0.43 -0.59 -1.04 -1.06 0.74 26 95 14 70.41 37.17 212 0.90 -0.90 -0.00 1.21 -0.30 0.13 27 72.3 35 92.99 24.75 102 1.12 -0.18 -0.94 0.51 0.10 0.64 25 X Y 70.96 36.33 98 1.34 -1.13 -0.20 -0.47 0.06 -0.62 27 68.5 34 70.70 35.92 120 3.14 -3.54 0.40 1.08 0.88 -1.15 25 68.7 33.2 86.77 30.82 15 -0.07 -1.33 1.40 -0.26 0.18 0.30 25 86.77 31.3 91.96 34.58 15 -0.85 -1.46 2.31 1.72 -1.37 3.87 25 92.3 33.9 93.94 24.58 75 -0.89 -1.22 2.11 -0.51 0.64 1.96 25 93.4 22.8 71.97 36.59 98 1.45 -0.99 -0.46 -0.18 0.56 -1.00 25 69.5 35.2 94.89 25.19 100 7.09 -5.24 -1.85 -0.64 -3.12 5.37 26 94.8 23.8 86.64 26.52 35 0.07 -0.93 0.86 1.42 -1.59 0.10 26 86.8 26.1 91.70 34.17 15 0.19 -1.60 1.40 -0.82 -0.74 1.75 25 92.1 33.3 94.95 24.42 130 2.02 -1.58 -0.44 -2.09 -1.01 1.01 25 94.8 24.7 92.10 37.60 15 0.68 -1.24 0.56 -0.35 0.16 0.49 25 X Y 70.84 36.56 114 1.75 -2.94 1.19 -0.70 -1.09 -0.05 25 70 32 72.85 37.04 18 -1.26 -0.42 1.67 0.84 -0.75 -0.59 25 X Y 70.61 36.68 217 2.28 -1.90 -0.38 3.11 -0.54 0.34 25 72 36.7 93.93 8.14 21 -0.14 -0.58 0.72 0.10 0.06 1.35 25 93.9 9.3 96.18 23.61 21 0.49 0.18 -0.67 1.18 0.55 2.76 26 97 24 70.23 36.01 126 1.25 -1.07 -0.17 1.85 -0.09 -0.24 26 72 34 70.74 36.12 228 0.91 -1.14 0.23 0.22 0.26 -0.03 26 73 34 78.24 30.22 15 0.68 -0.54 -0.14 1.49 -0.57 0.44 26 78 30.8 71.27 32.95 15 0.24 -0.22 -0.02 1.31 0.52 -0.13 25 X Y 96.03 23.95 23 -0.13 0.67 -0.55 1.10 -0.53 2.83 25 95.7 21.8 90.30 29.46 15 -1.66 -0.12 1.78 0.12 0.19 0.47 25 92.9 28.6
12. 12. 93.50 9.22 90 0.32 -1.08 0.76 -0.33 -0.43 0.19 25 94 10.2 87.64 28.87 15 -2.09 -0.39 2.48 -0.83 -0.21 0.09 25 87 28 70.47 36.48 214 2.71 -2.38 -0.32 2.26 -1.06 0.31 26 73.7 33.2 76.55 18.11 15 2.10 -1.63 -0.47 -0.31 -0.55 0.93 25 X Y 97.40 24.80 15 -1.19 1.20 -0.01 1.02 -0.17 -0.30 25 X Y 94.17 20.45 49 -0.73 -3.15 3.88 3.48 -4.18 -0.74 25 95.7 20.8 71.00 36.34 254 3.30 -1.13 -2.16 0.05 0.68 -1.02 25 72 35.8 94.97 24.76 146 1.59 -1.47 -0.11 -0.81 -0.61 0.15 25 95.3 25.5 95.02 24.83 148 4.12 -3.59 -0.53 0.54 -2.03 1.98 25 95.7 26.3 70.45 36.18 238 1.62 -1.80 0.18 -1.39 -0.26 -0.22 25 68.5 35 77.86 35.45 15 -0.24 0.28 -0.05 -0.90 -0.60 2.16 26 77.4 35.2 68.13 29.74 15 2.24 -2.41 0.17 4.58 0.54 0.53 26 68.5 28.7 70.68 36.51 189 4.09 -4.13 0.04 1.09 2.28 -1.40 25 72.5 33 86.96 35.33 16 -0.24 -0.74 0.97 0.06 0.85 1.89 27 X Y 92.70 22.21 54 0.32 -0.62 0.29 -1.20 -0.15 0.84 25 X Y 70.88 36.50 244 2.07 -0.10 -1.97 -0.41 3.38 0.02 25 71.2 32 70.08 37.38 24 0.56 -5.32 4.76 2.06 0.57 -5.74 25 X Y 79.21 30.38 15 1.58 -1.83 0.25 6.84 -3.18 0.84 25 79.2 30.5 70.81 36.48 237 5.05 -0.52 -4.53 0.87 3.75 -1.59 25 69.8 33.5 97.15 26.70 37 2.21 -0.58 -1.63 0.25 -2.08 2.49 25 97.15 27.2 70.24 23.63 20 2.34 -3.16 0.82 1.34 1.39 0.11 27 71.1 23 70.62 36.41 193 1.41 -1.68 0.28 -0.14 0.60 -0.27 25 68.5 32.3 92.91 35.80 15 -0.58 1.65 -1.07 -0.82 3.09 4.78 27 X Y 70.42 36.57 228 9.00 -8.16 -0.84 8.62 -2.96 2.05 26 71 34 69.06 36.28 15 1.31 0.47 -1.78 0.10 -0.40 -0.23 25 X Y 93.17 13.33 22 4.42 1.15 -5.57 -3.10 2.16 -0.63 25 95.2 14.9 74.66 35.52 15 -2.97 1.15 1.82 -2.06 -0.70 1.16 25 X Y
13. 13. 96.45 37.53 16 3.43 -2.87 -0.57 1.99 -1.01 1.37 25 96 36.6 93.35 12.16 84 0.35 -0.40 0.05 -0.17 -0.80 0.89 25 93.3 10.9 95.72 19.86 16 1.81 1.51 -3.32 2.58 -0.06 7.71 25 X Y 89.35 34.00 12 -0.88 -0.28 1.16 -0.10 -0.06 0.52 25 X Y 70.84 36.52 183 3.41 -4.41 1.00 3.66 3.19 -0.54 25 73.2 32.2 83.78 30.56 13 -2.14 -0.22 2.36 -0.39 -0.03 -0.61 25 84 29.5 92.45 8.58 12 0.94 -0.12 -0.81 0.02 -0.27 0.32 26 93.8 8.3 94.11 8.91 33 3.80 -3.19 -0.60 0.54 1.57 -0.56 25 94.8 8.5 92.63 13.59 27 -3.12 0.54 2.58 1.38 0.30 0.66 25 94.7 13 92.84 13.49 14 0.75 1.36 -2.10 1.37 -0.22 0.57 25 91.3 13.7 93.97 9.12 12 -0.94 -0.20 1.14 0.48 -0.50 0.34 25 94.9 9.6 83.77 30.24 12 -2.96 -0.64 3.59 0.03 -0.25 -0.75 25 82 30.5 73.47 34.38 12 2.61 -1.27 -1.33 1.43 0.36 1.26 27 73.1 36 73.12 34.70 12 5.20 -2.38 -2.82 1.61 -0.18 2.51 25 74 35 92.17 11.83 12 0.47 0.12 -0.59 0.14 -1.48 0.06 25 91.1 12.7 92.11 10.70 22 1.00 0.05 -1.04 0.55 -1.93 0.27 25 91 11.8 92.30 8.03 12 1.38 -0.30 -1.08 0.01 -0.90 0.63 25 90.7 8.3 81.97 34.33 24 -0.53 -1.25 1.78 0.01 -0.10 -0.25 25 83 32.8 85.32 32.30 13 -4.34 -0.74 5.08 0.56 -0.18 1.81 25 X Y 81.37 35.43 12 -4.92 -0.36 5.29 1.25 0.82 1.09 26 81.37 36.2 91.82 10.92 17 -0.56 -0.41 0.97 -0.19 0.16 0.24 26 90.6 10.9 91.80 10.90 12 -1.25 -0.04 1.29 0.83 -0.39 0.51 25 94 12.3 91.83 10.96 16 -0.58 -1.76 2.34 -0.32 0.25 0.30 25 90.4 9.9 97.99 24.92 18 -0.07 0.36 -0.28 0.24 0.05 1.25 25 97.99 26 83.51 30.61 17 -1.02 -0.38 1.40 -0.56 0.20 0.11 26 83 30 83.69 30.66 21 -0.27 -0.77 1.04 0.26 0.04 -0.53 25 84 32.5 90.50 29.66 12 -2.76 -0.65 3.41 -0.68 0.59 1.83 25 91.2 29.3
14. 14. 95.75 37.51 27 2.51 -3.48 0.97 2.49 -0.99 0.20 25 94.8 36.7 92.94 14.16 22 -1.51 0.49 1.03 0.38 0.43 1.43 27 92 15.8 95.76 37.64 12 2.34 -2.64 0.30 1.49 -0.18 0.98 25 93.9 37.1 91.63 27.20 12 0.33 -0.45 0.12 1.80 -0.22 0.08 25 90.6 26.5 91.86 8.05 20 0.11 -1.12 1.01 0.00 -0.33 -0.39 25 93 9.1 92.76 13.58 30 -0.50 -0.13 0.62 0.10 -0.38 0.93 26 91.6 14.7 96.79 33.05 16 -0.38 2.24 -1.86 -1.05 0.19 1.10 26 96 32.3 96.53 33.18 18 -0.30 1.22 -0.93 -0.57 -0.50 0.94 25 97 32 93.70 11.16 128 2.33 -4.03 1.70 -4.21 -1.88 2.66 25 94.2 11.16 70.79 36.44 208 2.55 -2.08 -0.47 0.86 1.39 -0.81 25 72.1 32.1 94.68 24.46 104 1.81 -2.68 0.87 0.05 -1.37 1.47 25 96.5 26.8 70.62 36.45 210 0.78 -0.66 -0.12 0.75 -0.52 0.23 25 71.8 37.6 88.35 27.44 46 -0.41 -2.32 2.73 0.90 -0.12 -0.63 26 X Y 82.52 35.88 17 -1.96 -0.58 2.54 0.79 -0.50 0.59 25 X Y 96.03 22.73 17 -0.04 0.12 -0.09 1.36 0.18 1.93 26 X Y 82.57 36.22 18 -0.28 -2.23 2.51 0.27 -0.05 1.60 26 83.8 35.5 88.09 18.10 58 0.00 -1.60 1.60 0.12 0.18 0.42 25 X Y 85.37 27.77 12 1.73 -1.79 0.06 7.52 -0.59 0.45 27 84.7 27 84.88 27.92 16 0.49 -0.61 0.13 1.48 0.12 0.25 26 83.7 27.4 85.96 27.56 17 0.49 -0.61 0.12 1.65 -0.23 0.20 26 85.7 26.45 86.10 27.56 12 2.64 -2.54 -0.10 8.52 -0.44 1.21 26 86 25.55 86.31 27.39 18 1.26 -1.54 0.29 1.75 0.16 0.43 25 86.9 25.3 82.03 33.03 10 -1.91 -6.36 8.27 2.62 -3.12 -0.29 24 X Y 80.32 29.58 15 1.02 -1.39 0.36 5.06 -1.34 0.36 24 82.5 28.5 81.11 28.96 10 1.64 -1.75 0.11 1.41 -0.21 0.27 24 81.5 29.2 95.53 29.24 40 0.87 -0.21 -0.66 -3.71 1.50 1.20 24 95 29.7 83.77 29.30 34 -0.33 0.06 0.28 -0.72 1.93 1.76 24 82.9 27.8
15. 15. 88.32 29.77 15 -3.29 -0.43 3.72 -0.43 -0.09 -0.00 24 90.2 29.7 80.29 29.43 15 1.23 -1.29 0.07 1.69 -1.09 0.70 24 79.8 30 80.22 23.06 38 3.55 -4.14 0.59 3.47 2.52 -0.71 24 X Y 85.39 28.60 33 -1.72 -0.21 1.93 -0.20 1.10 0.34 24 84.9 29 88.47 29.83 15 -4.30 0.27 4.03 0.06 2.18 0.81 24 89.2 30.1 88.31 29.86 15 -6.08 -0.95 7.04 -1.64 0.14 -0.29 24 88.5 30.6 70.61 23.61 15 4.92 -5.07 0.15 0.79 1.25 0.25 24 71.5 24 81.75 29.61 15 0.18 -0.34 0.16 2.14 -0.53 0.06 24 82 28.7 81.25 30.13 15 -2.31 -0.48 2.79 -1.50 -0.14 0.24 24 80.5 29.5 95.91 29.26 33 -0.08 -1.66 1.73 -0.43 0.39 1.46 24 96 29.8 80.97 30.88 12 -1.46 -1.31 2.77 -0.37 -0.36 -2.47 24 82 32.2 94.72 28.81 19 0.42 -0.88 0.47 6.89 -0.32 -0.57 24 94 29.6 70.35 23.25 30 0.80 -2.51 1.71 0.54 -0.62 1.01 24 70.5 22 90.67 31.61 23 -0.49 -3.66 4.15 0.56 0.42 1.48 24 91.2 33 94.30 23.31 34 2.22 0.85 -3.07 0.14 -0.33 -0.52 24 94 23.3 96.27 33.06 25 0.11 1.78 -1.89 -0.65 -0.82 1.01 24 95 32.5 95.77 19.06 12 2.60 -1.33 -1.27 0.28 0.06 2.14 24 95.5 18.5 83.69 30.66 21 -0.27 -0.77 1.04 0.26 0.04 -0.53 25 83.1 32 90.57 29.76 15 -0.84 -0.44 1.28 -0.49 0.49 1.43 24 92 29 86.10 31.05 28 -0.64 -5.72 6.37 1.71 0.67 0.45 24 86.2 31.8 86.28 29.31 19 -2.09 -0.75 2.83 -0.02 -0.15 -0.07 24 85.8 28.6 78.09 35.62 19 -0.95 0.06 0.89 0.32 -0.41 1.98 24 78.4 34.9 76.62 35.27 12 -2.21 2.18 0.03 -0.29 -2.18 6.15 23 X Y 70.49 21.04 12 0.22 -4.64 4.42 1.51 2.09 1.94 23 70.7 20.1 77.53 35.06 21 -1.22 0.17 1.05 0.44 -2.73 3.89 23 78.8 35.7 70.64 26.99 39 0.47 -4.65 4.19 -2.86 -1.14 3.13 23 X Y 77.23 35.72 111 2.23 -0.57 -1.66 7.52 -0.43 2.29 23 77.8 35.9
16. 16. 70.44 20.98 12 0.02 -4.45 4.42 2.98 0.53 1.98 23 69.8 20.5 73.75 34.88 18 2.94 -0.51 -2.43 -0.62 2.50 -2.17 23 74.4 34 75.60 33.02 20 2.23 -1.08 -1.14 2.17 -1.21 1.23 24 75.3 33 75.95 33.09 22 5.26 -3.62 -1.64 2.32 0.94 3.25 23 76.8 32.6 75.71 33.10 26 3.58 -2.75 -0.82 3.38 0.00 1.80 23 76 32.6 The focal mechanism solutions are plotted in the map using GMT software and various zones have been mapped from the clusters of similar focal mechanism. The radius of the beach balls shown in figure 1 represents the size of the earthquake. Bigger the size of beach balls corresponds to higher magnitudes. Different Zones and their characteristic faults: Zone 1: This zone covers the earthquakes occurred at Hindu Kush area. These are mostly Thrust faults. Zone 2: It covers the earthquakes occurred at the boundary of Jammu and Kashmir and China. These are Strike-Slip faults. Zone 3: It covers the Tibet region. These are Strike-Slip faults. Zone 4: It covers the Himalayas. These are Strike Slip faults. Zone 5: It covers Jammu and Kashmir. These are Thrust faults. Zone 6: It covers Uttarakhand and Nepal. These are Thrust faults. Zone 7: It covers the boundary of Nepal and Himalayas. These are Normal faults. Zone 8: It covers the Himalayas. These are Normal faults. Zone 9: It covers the Tibet region. These are Strike-Slip faults.
17. 17. Zone 10: It covers the Tibet region. These are Thrust faults. Zone 11: It covers the earthquakes occurred in Arunachal Pradesh. These are Thrust faults. Zone 12: It covers the boundary of NE India and Myanmar. Here the fault type is Thrust fault. Zone 13: It covers the earthquakes occurred in Myanmar. These are Strike-Slip faults. Zone 14: This zone covers the earthquakes of Andaman and Nicobar region. These are Thrust faults. Zone 15: It covers the Andaman and Nicobar region. The fault type is Thrust fault. Zone 16: It covers the Andaman and Nicobar region. These are Strike-Slip faults. Zone 17: It covers the Andaman and Nicobar region. These are Thrust faults. Zone 18: It covers Andaman and Nicobar region. These are Normal faults. Zone 19: It covers the earthquakes occurred in Madhya Pradesh and Western Maharashtra. These are Thrust faults. Zone 20: This zone covers the earthquakes of Gujrat and Rajasthan. These are Strike- Slip faults. Zone 21: It covers Sikkim and Bhutan. The fault type is Strike-Slip fault.
18. 18. Fig 1: Map showing Different Zones
19. 19. Another map is plotted showing the Pressure and Tension axes. Pressure axis Tension axis Fig 2: Focal Mechanisms with Pressure and Tension axes
20. 20. DISCUSSION AND CONCLUION The upper mantle beneath the mountainous Hindu Kush region of northeastern Afghanistan is the site of a tectonically complex area. Although it is not clearly associated with any island arc system, this region is perhaps the most active zone of intermediate depth (70-300km) earthquakes in the world. The region is therefore interesting, since it provides a setting for examining deep-seated tectonic processes in a collision zone as well as allowing a study of intermediate depth seismicity as phenomenon in it. Because of its proximity to the Eurasian- Indian plate boundary the Hindu- Kush seismic zone is believed to be grossly related to the convergence of the Indian and Eurasian sub-continents. We have two different types of fault plane solution in Hindu Kush region. Fault planes with solutions that in the west have westward plunging T axes and in the east have eastward or vertically plunging T axes. We infer that the configuration of the Hindu Kush seismic zone could possibly be the result of subduction of oceanic lithosphere from two separate, small basins in opposite directions. The thrust type faulting is prevalent in the Nepal region and confirmed that the under thrusting of Indian plate towards the north along the Himalayan arc has occurred. It is observed thrust and strike slip components and inferred that there is under thrusting of Indian plate towards southwest. Some fault-plane solutions of Tibetan region and observed that there is a presence of a combination of normal and strike-slip faulting with T-axes trending approximately east-west. There is a coherent under thrusting of Indian plate beneath the Lesser Himalaya in the eastern half of the arc. They inferred that slip vectors are locally perpendicular to the Himalayan mountain range with very gentle plunge in the eastern section and more steeply in the western section. It is apparent that the compressive stress is acting in N-S to NESW directions which are
21. 21. approximately perpendicular to the major trend of the Himalaya. It also reveals that the earthquake generation process in the region is due to the northnortheast compressive stress exerted by the Indian plate to the Tibetan plate. However, the plunges of P-axis of a few events show compression from approximately northwest direction. In the NE region near Nagaland and Manipur we have found from the focal mechanism and orientation of P and T axes that the CMF, a geologically older thrust fault, accommodates motion through dextral strikeslip manner, which is a part of relative plate motion between the India and Sunda plates. Therefore, CMF is the present-day active deformation front or plate boundary fault between the India and Burma plates. In Andaman region the strike slip events can hardly be designated as inter-plate events due to (i) the their deep occurrence well within the underlying Indian plate zone, and (ii) because of their nearly vertical fault planes oriented NW and NE respectively, contrasting with the shallow dipping NS trending decollement plane in the India-Burma subduction zone. Earthquakes with a similar mechanism do occur in the Andaman arc region, except that they are associated with the transform faulting in the Andaman sea, the Sumatran fault zone to the east or the NS trending right- lateral strike-slip faulting along the Sagaing fault zone farther east. Hence, these strike-slip events are distinct from the above mechanisms and are seen to be associated with intra-plate deformation in the subducting Indian plate. The focal mechanisms of earthquakes in Gujrat region were the result of movement in a fault at shallow depth, caused by the stress within the Indian tectonic plate pushing northward into the Eurasian plate. They are also called intraplate earthquakes as they occur in the interior of a tectonic plate different that those Himalayas earthquakes that occur at the plate boundary.
22. 22. REFERENCES Principles of Seismology: Agustn Udas Lecture Notes Focussing on MICROEARTHQUAKE INVESTIGATIONS: NGRI, Hyderabad Discourse on Seismotectonics of Nepal Himalaya and Vicinity: Appraisal to Earthquake Hazard by D. Shanker1, Harihar Paudyal, H. N. Singh