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Fault Plane Solutions and Evaluation of Stress
Pattern of Seismotectonically Active Sumatra-
Andaman Subduction Zone
Hamid...
AIM AND OBJECTIEVES:
To enumerate the focal plane solutions of Andaman and
Nicobar islands based on earth quake parameter...
STUDY AREA:
METHEDOLOGY:
1. Data archiving focal plane solutions
2. Data archiving b Values.
3. Ground Penetrating Radar Survey
1. Data archiving focal plane solutions
In order to determine where and what depth an earth quake
has occurred, it is pos...
Beach Balls For Various Faults
For the present study faults are identified from the focal mechanism of earth quake
data from International center for sei...
b value analysis
 b value tells about the relative occurrence of large and small earthquakes during a
particular year in ...
 If the b value is less for a region it indicates that there is a possible chance of large
magnitude earthquakes for that...
 The earth quake data were archived from USGS and magnitudes above 5.0 are
analysed.
 In the present work the whole Anda...
RESULTS AND DISCUSSION
 The earthquake focal mechanism data of Andaman and Nicobar Islands between 1977
and 2004 were acq...
Angle of dip Fault
0o<45o Thrust fault, compressional,
reverse fault
45o to 90o Normal fault, tensional fault,
gravity fau...
The azimuth or structural trend of all the earthquakes were plotted by
using the Geo-Orient/stereo net 7, in the form of R...
 The strike of the faults trends in NNE-SSW, NNW-SSE, NE-SW, E-W and NW-SE direction.
 The direction of Principle stress...
Major tectonic features and fault plane solutions for the earthquakes
(Magnitude 6.0 and above) occurred between 1977 and ...
 In comparison to the trenchward earthquakes (12 numbers), the backarc
extension earthquakes are more numerous (19 number...
showing a sharp thrust contact between overriding sandstone
and the shale near Port Mout (N 110 38’678”; E 92o 39’ 40”)
b value analysis
 The earthquake data of Andaman and Nicobar Islands and its surroundings
were acquired from USGS (United...
Block Latitude Longitude
A 4o -6o N 90 o -96 o E
B 6.1o -8 o N 90 o -96 o E
C 8.1o -10o N 90 o -96 o E
D 10.1o -12o N 90 o...
BLOCK A
1
2
1 1 1
2
13 13
1 1
2 2
1984 1987 1988 1989 1990 1991 2004 2005 2006 2007 2012 2013
no.ofevents
year
2
1 1 1 1
4
6
2
11
1
0
2
4
6
8
10
12
1928 1934 1946 1964 1973 2004 2005 2006 2008 2010
no.ofevents
year
BLOCK B
2
1 1
2 2 2
1 1 1
2
1
8
13
2 2
1 1
0
2
4
6
8
10
12
14
1939
1960
1961
1982
1983
1985
1986
1989
1990
1991
1993
2004
2005
200...
1
2
1 1 1 1 1 1 1 1 1 1 1 1
3
1 1 1 1
5
17
1
2
0
2
4
6
8
10
12
14
16
18
no.ofevents
year
BLOCK D
1
3
1 1 1 1 1
11
2
1 1
2
0
2
4
6
8
10
12
1928 1941 1962 1968 1978 1981 1983 2004 2006 2007 2008 2010
no.ofevents
year
BLOC...
year a value b value
1939 5.6 0.987
1960 5.2 1.121
1961 5.2 1.121
1982 5.5 1.06
1983 5.2 1.063
1985 5.2 1.121
1986 5.8 1.0...
year
a
value b value
1918 6.2 0.9596
1932 6 1.0267
1938 6.2 0.9596
1941 5.8 1.0258
1965 5.7 1.043
1967 5.7 1.043
1968 5.5 ...
BLOCK Cumulative b value
A 1.1274
B 0.9836
C 1.0168
D 1.0021
E 1.0946
 In latitudes between 4o-6o N (Block A) encircling Northern Sumatra, the
calculated b values which are less than 1 that a...
 In latitudes between 8.1 o to 10 o N (Block C) which includes Car Nicobar and
adjacent Islands, the estimated b value wh...
 The fault plane solutions for Andaman and Nicobar has identified mainly
three types of faults viz, Normal, Thrust and St...
 The b value analysis of Andaman and Nicobar Island suggests the
occurrence of future seismicity along the active regiona...
THANK YOU
QUESTIONS ??
focal plane solutions and stress pattern of Sumatra Andaman subduction zone
focal plane solutions and stress pattern of Sumatra Andaman subduction zone
focal plane solutions and stress pattern of Sumatra Andaman subduction zone
focal plane solutions and stress pattern of Sumatra Andaman subduction zone
focal plane solutions and stress pattern of Sumatra Andaman subduction zone
focal plane solutions and stress pattern of Sumatra Andaman subduction zone
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focal plane solutions and stress pattern of Sumatra Andaman subduction zone

  1. 1. Fault Plane Solutions and Evaluation of Stress Pattern of Seismotectonically Active Sumatra- Andaman Subduction Zone Hamid Hussain v & Balaji S PRESENTED BY: HAMID HUSSAIN V DEPT.OF DISASTER MANAGEMENT KUFOS
  2. 2. AIM AND OBJECTIEVES: To enumerate the focal plane solutions of Andaman and Nicobar islands based on earth quake parameters. (Epicenter, strike and dip angle) To estimate the b value for Andaman and Nicobar islands using earth quake magnitude data and epicenter data. To analyse the fault slip rate/stress accumulation on Regional seismogenic faults.
  3. 3. STUDY AREA:
  4. 4. METHEDOLOGY: 1. Data archiving focal plane solutions 2. Data archiving b Values. 3. Ground Penetrating Radar Survey
  5. 5. 1. Data archiving focal plane solutions In order to determine where and what depth an earth quake has occurred, it is possible to make a fault plane solution/focal mechanism solutions which is deducing the orientation of fault plane and direction of displacement of that plane. These are found from the first arrivals at a number of receivers encircling the epicenter.
  6. 6. Beach Balls For Various Faults
  7. 7. For the present study faults are identified from the focal mechanism of earth quake data from International center for seismology (ICS) by analyzing the strike, dip, magnitude, and epicenter of the earthquakes.  Only the earthquakes which has a magnitude above 6.0 were considered for the analysis.  The azimuth or structural trend of all the earthquakes were plotted using the Geo-Orient/stereonet7 in the form of Rose diagram.  The orientation and direction of strike were inferred and the direction of principle stresses were identified from the strike bearings.  The epicenter of the earth quake that occurred from 1977-2005 and subsequent focal plane mechanisms were plotted in the map using Arc Gis version 9.3  Each faults were identified in relation with the regional fault systems.  The results were analysed.
  8. 8. b value analysis  b value tells about the relative occurrence of large and small earthquakes during a particular year in a particular area.  Its given by the relation Log N = a – bM  N = Number of Events  a = a constant, which is the highest Magnitude of the occurred earthquake during a particular year.  M = magnitude of the Earthquake.  This Relation is popularly known as Guttenberg Ritcher Relation
  9. 9.  If the b value is less for a region it indicates that there is a possible chance of large magnitude earthquakes for that region.  If the b value is high there is a possibility of occurrence of small magnitude earthquake more than high magnitude earthquakes or less probability of large earthquake in compared to small ones.  b value tells about the accumulation of stress also.
  10. 10.  The earth quake data were archived from USGS and magnitudes above 5.0 are analysed.  In the present work the whole Andaman and Nicobar Islands were divided in to 5 blocks according to latitude and longitudes , b values and corresponding a values were calculated for the years 1918-2014.  The b values for each block were plotted in the map by using Arc Gis version 9.3.  The b values showing exceptional values are then analysed in association with the regional fault systems.  The results are analysed.
  11. 11. RESULTS AND DISCUSSION  The earthquake focal mechanism data of Andaman and Nicobar Islands between 1977 and 2004 were acquired from International Centre for Seismology (ICS), UK. Magnitudes of greater than 6.0 were used for the study purpose. A number of 35 earthquakes were collected, analysed and plotted. Characteristic seismogenic faults were interpreted from the earthquake data using strike, dip, magnitude, and epicenter of each earthquake. FOCAL MECHANISM SOLUTIONS
  12. 12. Angle of dip Fault 0o<45o Thrust fault, compressional, reverse fault 45o to 90o Normal fault, tensional fault, gravity fault ≈90o Strikeslip fault, transcurrent fault, lateral fault Block modal for fault identification on the basis of angle of dip (Bath, 1979)
  13. 13. The azimuth or structural trend of all the earthquakes were plotted by using the Geo-Orient/stereo net 7, in the form of Rose diagram. Rose diagram showing the strike of the faults and their prevalence Dip direction of the faults in stereo net
  14. 14.  The strike of the faults trends in NNE-SSW, NNW-SSE, NE-SW, E-W and NW-SE direction.  The direction of Principle stresses were identified  NNW-SSE, indicating the direction of maximum principal stress (σ1)  NE-SW, indicates the direction of least principal stress (σ3)  All the dips are trending towards Easterly direction
  15. 15. Major tectonic features and fault plane solutions for the earthquakes (Magnitude 6.0 and above) occurred between 1977 and 2005. Thick red line With triangles indicates the Trench (AST), black line indicates West Andaman Fault (WAF) and thick red line indicates Andaman Backarc Spreading Center (ABSC)
  16. 16.  In comparison to the trenchward earthquakes (12 numbers), the backarc extension earthquakes are more numerous (19 numbers), suggesting active down-dip extension of the pre-seismic plate boundary.  Six earthquakes observed were ruptured on West Andaman Fault (WAF) which is deep seated active strikeslip fault and is acting as lithospheric scale boundary. Subsequently, six earthquakes were observed along Andaman Backarc Spreading Centre (ABSC).  Twelve number of trenchward earthquakes were observed in the vicinity of the subduction zone due to tectonic activity along the trench.  Three earthquakes ruptured along Seulimeum strand of Sumatra fault system East of ABSC.
  17. 17. showing a sharp thrust contact between overriding sandstone and the shale near Port Mout (N 110 38’678”; E 92o 39’ 40”)
  18. 18. b value analysis  The earthquake data of Andaman and Nicobar Islands and its surroundings were acquired from USGS (United States Geological Survey) and ICS (International Centre for Seismology) website. The data from 1918 to 2014 were collected and only the magnitudes 5.0 and above were taken for the analysis.
  19. 19. Block Latitude Longitude A 4o -6o N 90 o -96 o E B 6.1o -8 o N 90 o -96 o E C 8.1o -10o N 90 o -96 o E D 10.1o -12o N 90 o -96 o E E 12.1o -14o N 90 o -96 o E BLOCK WISE CALSSIFICATION OF STUDY AREA
  20. 20. BLOCK A 1 2 1 1 1 2 13 13 1 1 2 2 1984 1987 1988 1989 1990 1991 2004 2005 2006 2007 2012 2013 no.ofevents year
  21. 21. 2 1 1 1 1 4 6 2 11 1 0 2 4 6 8 10 12 1928 1934 1946 1964 1973 2004 2005 2006 2008 2010 no.ofevents year BLOCK B
  22. 22. 2 1 1 2 2 2 1 1 1 2 1 8 13 2 2 1 1 0 2 4 6 8 10 12 14 1939 1960 1961 1982 1983 1985 1986 1989 1990 1991 1993 2004 2005 2006 2007 2010 2012 no.ofevents year BLOCK C
  23. 23. 1 2 1 1 1 1 1 1 1 1 1 1 1 1 3 1 1 1 1 5 17 1 2 0 2 4 6 8 10 12 14 16 18 no.ofevents year BLOCK D
  24. 24. 1 3 1 1 1 1 1 11 2 1 1 2 0 2 4 6 8 10 12 1928 1941 1962 1968 1978 1981 1983 2004 2006 2007 2008 2010 no.ofevents year BLOCK E
  25. 25. year a value b value 1939 5.6 0.987 1960 5.2 1.121 1961 5.2 1.121 1982 5.5 1.06 1983 5.2 1.063 1985 5.2 1.121 1986 5.8 1.005 1989 5.4 1.079 1990 6 0.971 1991 5.9 0.987 1993 5.7 1.022 2004 7 0.937 2005 6.5 0.949 2006 5.8 1.032 2007 5.9 1.005 2010 7.8 0.747 2012 5.5 1.06 Year a value b value 1984 5.2 1.1 1987 5.6 1.025 1988 5.8 0.989 1989 5.3 1.83 1990 5 1.148 1991 5.2 1.103 2004 8.6 1.185 2005 6.2 0.941 2006 5.1 1.125 2007 5.4 1.062 2012 5.6 1.034 2013 5.9 0.9895 BLOCK A BLOCK B
  26. 26. year a value b value 1918 6.2 0.9596 1932 6 1.0267 1938 6.2 0.9596 1941 5.8 1.0258 1965 5.7 1.043 1967 5.7 1.043 1968 5.5 1.081 1970 5.5 1.081 1986 5.6 1.062 1992 5.9 1.008 2004 6.1 1.03 2005 7.2 0.943 2009 6.1 0.975 2012 5.8 1.025 year a value b value 1928 8 0.934 1934 6.5 0.986 1946 6.7 0.956 1964 6.3 1.017 1973 5.6 1.44 2004 5.8 1.113 2005 6 1.076 2006 5.9 1.035 2008 6.7 1.044 2010 6.6 0.971 year a value b value 1928 6.2 0.983 1941 7.7 1.75 1962 6.1 1 1968 5.5 1.1 1978 5.6 1.08 1981 5.7 1.07 1983 6.1 1 2004 6.2 0.996 2006 6.9 1.051 2007 5.6 1.089 2008 5.8 1.051 2010 6.8 0.956 BLOCK C BLOCK D BLOCK E
  27. 27. BLOCK Cumulative b value A 1.1274 B 0.9836 C 1.0168 D 1.0021 E 1.0946
  28. 28.  In latitudes between 4o-6o N (Block A) encircling Northern Sumatra, the calculated b values which are less than 1 that are parallel to the strike of West Andaman Fault (WAF) suggest accumulation of potential stress and severity and probability of future earthquakes by rupturing the segment of the fault accompanied by stress release.  In latitudes between 6.1o to 8 o (Block B) which includes Great Nicobar and Nancowry group of Islands, the estimated b values are less than 1 and 6 numbers of this kind falls along ABSC and 6 numbers fall parallel to WAF and 7 numbers fall in the vicinity of subduction zone (AST). These tectonically active features (ABSC, WAF, and AST) provide an ideal tectonic settings for the occurrence of future seismicity.
  29. 29.  In latitudes between 8.1 o to 10 o N (Block C) which includes Car Nicobar and adjacent Islands, the estimated b value which are less than 1.0 along WAF-5, ABSC-3 and AST-5 and are at risk for the occurrence of mega earthquakes.  In latitudes between 10.1 o to 12 o N (Block D) yielded b values which are less than 1.0 around Little Andaman and South Andaman will probably experience moderate to large magnitude earthquakes in the future.  In latitudes between 12.1 o to 14 o N (Block E) which encircles Middle and North Andaman, the plotted b value are below the threshold magnitudes and the region is highly susceptible for future tectonic activities especially along tectonically active Jarwa thrust, Button thrust and in the vicinity of active faults.  The estimated cumulative b value of Block B (Great Nicobar and Nancowry group of Islands) show exceptionally low b values (0.9836) which is suggesting that these regions are more vulnerable for future seismicity along tectonically active faults.
  30. 30.  The fault plane solutions for Andaman and Nicobar has identified mainly three types of faults viz, Normal, Thrust and Strike slip.  Based on the earthquake focal mechanism analysis, it was found that most of the earthquakes are ruptured in the forearc and backarc region than trench ward region in the Western side of the Islands, this is suggesting that the West Andaman Fault (WAF) is acting as a lithospheric scale boundary and the back arc region is in the state of down dip extension.  Most of the earthquakes falling in the back arc region suggests that the region is active, as evidenced by the opening of the Andaman Sea. CONCLUSION
  31. 31.  The b value analysis of Andaman and Nicobar Island suggests the occurrence of future seismicity along the active regional faults i.e. the low b values corresponding to the vicinity of regional active fault systems such as WAF, ABSC and AST will experience future seismicity by rupturing the segments of the faults accompanied by stress release.
  32. 32. THANK YOU
  33. 33. QUESTIONS ??

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