This document summarizes information about potential earthquake zones in the Indian Ocean, including: 1) It discusses different types of plate boundaries like convergent, transform, and divergent boundaries that can cause submarine earthquakes. The Great Sumatran fault and Owen fracture zone are given as examples. 2) It describes triple junctions, which are points where three tectonic plates meet, and aulacogens, which are failed triple junction arms that can cause massive earthquakes. The Rodrigues triple junction in the Indian Ocean is mentioned. 3) It provides an overview of seismic waves that propagate in the ocean, like t waves, and sensors like ocean bottom seismometers, geophones, and

1. Potential earthquake zone of indian ocean
By :- Chavda hitesh harshadbhai
Roll.no:-04
Department of marine science
Msc Marine Science , Part-2
Goa university

2. contents
Understanding submarine earthquake
Understanding Tsunami
Triple junction in Indian Ocean
Concept of Aulacogen
Seismic waves in ocean
Ocean bottom seismometer
Sensors :-Geophone ,hydrophone
Measurement of earthquake
Case Study

3. Sub-marine earthquake
Underwater earthquake occur at the bottom of ocean
Leading to cause tsunami
 plate tectonics helps to explain the cause of submarine earthquakes
I. Convergent plate boundary
 older, and denser plate moves below the lighter plate.
 Ex:-Great Sumatran fault
II. Transform plate boundary
 two plates will slide past each other
 Ex:-Owen fracture zone
III. Divergent plate boundary
 two plates are moving away from each other
 Ex:-Carlsberg ridge,90E ridge

4. Triple junction
*A point where the boundaries of three tectonic plates meet.
*Three boundaries will be one of 3 types - a ridge (R), trench (T)
or transform fault (F)
*The Rodrigues Triple Junction is a R-R-R triple junction in the
southern Indian Ocean, where the African, the Indo-Australian and
the Antarctic Plates meet.
*Potential zones for earthquake
Aulacogen:-An aulacogen is a failed arm of a triple junction.
-Cause massive earthquakes

5. SEISMIC WAVEs IN OCEAN
*Tertiary waves:- t waves ,acoustic wave
*Propagates efficiently in the ocean compared to seismic
waves..
* frequencies ranging from 4 to 50Hz.
*Travels in SOFAR channel with min. velocity 1.5km/s
*IT is recorded on SOFAR hydrophones, ocean bottom
seismometers (OBS) or seismographs
* Vp>Vs>Vt…..

6. Ocean bottom seismograph
Ocean bottom seismometer- Records earth motion under ocean &
lake
*Works on principal of inertia & Acoustic sounding
*Consists of two sensors 1.Geophone 2.Hydrophone
Types:-
1. Short-period OBSs:- long frequency,
2. Long-period OBSs:- short frequency
Working principle

7. Different sensors
Geophone:-Converts ground movement (velocity)
into voltage,z which converted in to digital signals
*Response of geophone is proportional to ground
velocity,
*geophones are used in reflection seismology to record the energy
waves reflected by the subsurface geology.

8. HYDROPHONE
*Microphone designed to be used underwater for recording
or listening to underwater sound.
*Based on a piezoelectric transducer
*Convert a sound signal into an electrical signal since sound
is a pressure wave.

9. An analysis of 2004Sumatra earthquake fault plane mechanisms and Indian
Ocean tsunami
Journal:-Science

12. QUICK REVIEW
Dec 26, 2004: Magnitude 9.3 (moment mag)
• Undersea (depth 30 km)
• Epicentre of the W coast of Sumatra
• Tsunami followed, killing 230,000 in 14 countries
• Caused by subduction: A 1600 km faultline slipped ~15 m along
the subduction zone with the India plate slides under the Burma
plate (over several mins)
• Reverse faulting • The 2nd largest earthquake ever recorded on
a seismograph
• 24-30 m waves reaching the coasts • Total E of Tsunami = 5
megatons of TNT • More than twice the total explosive energy
used during all of WWII • Greatest strength waves was in the E-
W direction • Distance is NEVER a guarantee of safety, Somalia
was hit harder than Bangladesh • No warning systems were in
place • The tsunami in deep water is only recognizable by
expensive little sensors
• Coral reefs would have helped, they would have acted as a
barrier

13. reference
1. Ammon, C.J. et al. (2005). “Rupture Process of the 2004
Sumatra-Andaman Earthquake”. Science 308, 1133–1139.
2. 2. Borrero, J.C. (2005). “Field Data and Satellite Imagery of
Tsunami Effects in Banda Aceh”. Science 308, 1596.
3. 3. Harada, K. et al. (2005). http://www.drs.dpri.kyoto-u.ac.
jp/sumatra/thailand/phuket_survey_e.html#result.
4. 4. Ji, C. (2005). http://www.gps.caltech.edu/∼jichen/
Earthquake/2004/aceh/aceh.html.
5. 5. Lay, T. et al. (2005). “The Great Sumatra-Andaman
Earthquake of 24 December 2004”. Science 308, 1127–
1133.
6. 6. Liu, P.L.-F., Cho,Y.-S.,Yoon, S.-B. and Seo, S.-N. (1994).
“Numerical Simulations of the 1960 Chilean Tsunami
Propagation and Inundation at Hilo Hawaii”. In: El-Sabh,
M.I. (ed.), Recent Development in Tsunami Research.
Kluwer Academic Publishers, Dordrecht.
7. https://dosits.org/people-and-sound/examine-the-
earth/earthquakes/

14. Thank you