July, 2012 || Volume 16 No.3
Review Paper
Historical development of seismic imaging technique –
An OverviewScientist (Retd): National Geophysical Research Institute, Uppal Road, Hyderabad.
Home: 12-13-332, Street 12, Tarnaka, Hyderabad-500 017.
E-mail: rparvatareddy@yahoo.com; paravata@yahoo.comr
ABSTRACT
Old scriptures mention that early studies carried out by Rishis/sages have helped in developing various tools and techniques to unravel the mysteries associated with the Earth. Recognition of the ensuing events of disaster like storms, cloudbursts, fire etc. by prehistoric man was mostly done through sound and light waves .Like in the present day, his understanding of disasters like earthquakes was limited, as he was not having requisite knowledge to probe the interior of the earth. It is mentioned in some old scriptures that the ancient man tried to guess the location and onset of earthquake activity, from the unusual behaviour of some animals and insects.Varahamihira mentioned in Brihat Samhita that earthquake prediction can be done observing abnormal cloud formations. Specific details of their studies need to be extracted from earlier scriptures, to add to our knowledge base.
Even though sound waves have historically been used to understand vibrations of various frequencies, and to decipher signals coming from within the Earth, no systematic development in imaging the internal structure of the earth began until the mid 19th century. A concise exposition of the historical development of seismic imaging techniques is included in this article, to expose the reader to the focused studies carried out by eminent scientists of the 19th and early 20th centuries. The very fact that earlier studies combined theory and practice points out to the importance of these early studies and the strong scientific base they have created for subsequent developments. During the last 50 to 60 years considerable progress has been achieved not only in imaging basement structure but also sub basement crustal and sub crustal lithospheric structure. Theoretically supported experiments and their use in producing results help in holistically developing various scientific studies. Such a holistic development has been achieved in the seismic imaging of the subsurface formations extending from near surface depths to sub crustal columns. The basic objective in summarizing these chronological developments is to provide a broad understanding of the evolution and development of seismic imaging techniques (covering both analog and digital eras).Such an understanding is essential to properly use present day higher quality data acquisition and processing gadgets and would help producing high quality subsurface images, with time and space parameters as essential inputs. It is now well established that area specific attributes and time dependant variations alone can help in better understanding the intricate processes associated with subsurface structures and tectonics. The passive seismic based mega Arrays have indeed yielded excellent images of deep interior and provided useful information on the crust-mantle interactions. Global Array data and area specific 4-D seismic images of different dimensions, hopefully, would provide apt answers to many of the problems linked to the structure and evolution of the crust and sub crustal lithosphere
1
Pre- and post-seismic activities along the Myanmar-Andaman-Sumatra Subduction Margin: insights for tectonic segmentation
Prosanta Kumar Khan*, Anand Mohan and Suparna Chowdhury
Department of Applied Geophysics, Indian School of Mines, Dhanbad, Jharkhand, India
*Corresponding author. Email: pkkhan_india@yahoo.com
ABSTRACT
Spatial variation of the occurrences of large and great earthquakes along the subduction margin can be linked with various plate tectonics parameters viz. converging plate velocity vector, plate obliquity, age of the subducting plate, depth of plate flexing and inter-plate coupling. Present study addresses many of these parameters for understanding the seismotectonic status along the eastern subduction margin (i.e., Mayanmer-Andaman-Sumatra) of India analyzing earthquake dataset with magnitude mb > 4.5 taken from the Harvard Centroid Moment Tensor (CMT) catalogue for the period starting from January 01, 1976 to December 09, 2009. The dataset was divided into two categories: pre- and post-events based on the occurrence of 26 December 2004 off Sumatra mega-event (Mw = 9.3). The study area between Myanmar and Sumatra was divided into 12 sectors based on plate obliquity.
Analysis shows that area near Sumatra record highest seismicity concentration, and area past the north Andaman has least concentration, preceding the 2004 mega-event, and further increases marginally towards north. Instead, following the mega-event, concentration though decreases towards north, phenomenally reduces past the sector 7 (near the central part of the arc). The seismic moment energy release decreases more than two orders of magnitude past the sector 7 towards north during post-seismic deformation phase. It is, thus, may be inferred that stress energy was mainly confined between Sumatra and Andaman after the 2004 event. These observations are clearly accounted for tectonic subdivision of the margin into northern and southern near transition zone around the central part of the arc. It was also appreciated in the literature that the transition zone apparently countered spreading motion of the Andaman Sea in the back-arc area. It was furthermore reported that the 2004 off Sumatra mega-event rupture did not move further towards north past the North Andaman area. It is thus, may be proposed that the two arcs along this subduction margin are tectonically playing differently behind the generation of moderate earthquakes along this margin.
2
Wintertime mapping and monitoring of sea ice temperatures surrounding Antarctica using SSM/I data
T. J. Majumdar* and S. Bhattacharya
Space Applications Centre (ISRO), Ahmedabad – 380 015, India
*Corresponding author: E-mail: tjmajumdar@rediffmail.com
Abstract
The Polar Regions are known to be highly sensitive to warming effects of the increased greenhouse gases. Sea ice, together with land ice, exerts profound influence in controlling the global climate. Mapping and monitoring of sea ice concentration and sea ice temperature around Antarctica during wintertime have been attempted here with NASA Team Algorithm. Results obtained concur well with those obtained by other workers. Major sea ice concentrations vary between 80-100% during August 2002 with more number of classes and sea ice temperatures are found in the range of 230 to 250 K.
3
The solar influence on the monsoon rainfall over Tamil Nadu
R. Samuel Selvaraj and Raajalakshmi Aditya*
Presidency College, Chennai, India
* Government Arts & Science College, Tiruttani, India
E mail: rajvi99@gmail.com
ABSTRACT
We use 100 years data for studying correlative effects between solar cycle and rainfall over Tamil Nadu. For the period of different solar cycles, we compute the correlation coefficients for the seasonal months of Jan-Feb (JF), Mar-May (MAM), June-Sept (JJAS) and Oct-Dec (OND) and annual mean data. We find that: (i) with a moderate - to high significance; Tamil Nadu rainfall is correlated with the sunspot activity and (ii) there is an overall trend that during the period of high sunspot activity, occurrence of rainfall is low compared to the period of low sunspot activity.
We speculate in this study a possible physical connection between the occurrence of the rainfall and the sunspot activities and the flux of galactic cosmic rays. Some of the negative correlations between the occurrences of the sunspot and rainfall activities obtained for different solar cycle periods are interpreted as effects of aerosols on the rain forming clouds due to either intermittent volcanic eruptions or due to intrusion of interstellar dust particles in the earth’s atmosphere.
4
Study of Latitudinal variation of Ionospheric parameters - A Detailed report
Nuzhat Sardar, Anup K Singh1, Anju Nagar2, S.D Mishra3 and S.K. Vijay
Govt. Geetanjali Girls P.G. College Bhopal-462026, India.
1Department of Physics, Govt. P.G. College, Sehore-466001, India.
2Department of Physics, Govt. Science College, Gwalior-474003, India.
3Department of Physics, Govt. M.L.B, P.G. College Bhopal-462026, India.
Email: nuzhat_ahmed2006@yahoo.com
ABSTRACT
The ionospheric slab thickness is the ratio of ionospheric electron content (IEC) to the F-region peak electron density (NmF2). This has been analyzed during low solar activity period from January 2006 to December 2010. Hourly value of IEC and NmF2 by ionosonde technique is collected at Kwajelin (90N-1670E), Learmonth (220S-1140E); low latitude, Athens (380N-240E), Sanvito (400N-170E); mid-latitude and Chilton (520N-3590E), Port_Stanley (520S-3020E) high latitude location in the present study. The data and analysis method are classified in to 3 seasons including equinox (March, April, September and October), winter (January, February, November and December) and summer (May, June July and August). A detailed analysis of derived results is presented to bring into focus the latitudinal variations and utility of variations ionospheric parameters.
Book Review
The Nature of Precious Gemstones and Gems
By G.P. Kimothi,
Published by Professional Book Publishers,
Hyderabad, 132 p, 2012, Price Rs. 200/-
Embodying not only the basic scientific information such as crystal structures, optical and physical properties, chemical compositions, occurrences in specific geological settings and geneses of gemstones and gems of a large variety, and the Greek and Indian mythologies and common beliefs or superstitions associated with them – including influences of stars on the wearers of gems – the book also highlights the terms used by traders in northern and southern India, gradation and valuations, fashioning of gems, etc. This work thus brings science of the gems closer to the common man.
The richly colourful and captivating pictures of a large number of gems are extremely pleasing to the eyes and eloquently bring out their characteristics. Indeed, this work by an humble on-the-field geologist provides a wealth of valuable and relevant information, which the scientists, the lovers of gems and the commercial dealers will find interestingly important.
The making of substitute (artificial) gems and the comprehensive descriptions of their unique properties are discussed with finesse.
This book is written by an earth scientist who could have become a millionaire but chose to enrich the nation’s coffer by discovering diamonds in inhospitable terrains, under harsh and hostile conditions in many areas in India and in Africa.
I wish the author and the publisher had the manuscript vetted by a language expert and carefully done the proof-reading before sending the manuscript of this wonderful book to the press. I hope the second edition will ensure elimination of faulty constructions and printer’s devils which are galore.K.S. Valdiya
Jawaharlal Nehru Centre of Advance Scientific Research
Bangalore-560064
ANNOUNCEMENT
49th Annual Convention of Indian Geophysical Union
29-31 October 2012Venue: Pandit Deendayal Petroleum University Campus, Raisan Village,
Gandhinagar, Gujarat 382007
Topics of the convention:
Special Theme: Towards the Energy Security – Exploration, Exploitation and New Strategies
Other Themes:
1. Solid Earth Geophysics
2. Exploration, Engineering and Environmental Geophysics
3. Marine Geosciences
4. Theoretical and Experimental Geophysics
5. Atmosphere, Space and Planetary Sciences
6. Inter and Intra Plate Seismicity
Abstract submission: To be submitted electronically on or before 25th August 2012
http://germi.org/igu-abstracts.html
Contact details for the 49th annual convention
1. Dr. T. Harinarayana, Convener for IGU convention
Ph.: +91 79 23275365, Fax No.: +91 79 23275080,
E-Mail: Harinarayana@germi.res.in
2. Dr. P. Koteswara Rao
Ph.: +91 40 23434616, Fax: +91 40 27171564
Email: koteswara999@rediffmail.com; igu123@gmail.com
Contact details for post seminar IGU workshop:
1. Dr. Ajay Mangalik
Ph.: +91-40-23434684, Fax: +91 40 27171564
Email: ajay@ngri.res.in
2. Dr. Kapil Mohan
Ph.: +91 79 66739013, Fax: +91 79-66739015,
Email: kapil_geo@yahoo.co.in
For general information please visit www.igu.in
IGU AWARDS*-2012
Nominations are invited for the following Awards on or before 10th July 2012 to : igu123@gmail.com
1. Dr. M.S. Krishnan Gold Medal-2012
2. Decennial Award-2012
3. IGU-Hari Narain Life time achievement award in Geosciences- 2012.
(Please refer details: www.igu.in)
(*Only those Nominations received from the past recipient or present EC member of IGU will be considered)
For further details contact:
Dr. P. Koteswara Rao, Hon. Secretary-IGU, NGRI, Hyderabad.
Ph: 040-23434616, Email: igu123@gmail.com ; koteswara999@rediffmail.com.
