GIS based seismic hazard microzonation for Kochi city using ground-shaking site effects data

MICRO EARTH TREMORS IN KERALA

An interdepartmental discussion was conducted on March 24, 2002, at ACESS campus, to appraise and share views on the recent micro earth tremors in Kerala. Directors and senior level officers from
Geological Survey of India, Central Ground Water Board, India Meteorological Depart ment, State Ground Water Department and Directorate of Mining and Geology participated in the deliberations, besides the Scientists from CESS. These events have been recorded from Kannur in the north Kerala to Parassala in the south. However, significant damages have been re ported from Malappuram, Palakkad and Trichur districts in the north and Kollam and Alappuzha districts in the south. The manifestations and reports of these micro tremors collected from various localities were presented in the meeting. The observations include cracks in the buildings, oscillations and wavy formations in the open wells, anomalous fluctua tion in water table and perceptible ground cracks. Ground vibrations and unusual sounds were also noticed in very few localities. The present chain of events were found to occur from the month of January 2001 and isolated incidents are still being reported from different places in Kerala. However, most of the localities appear to have been affected duringthe month of February. Even though the affected localities are spread throughout the state, the felt area in each of the locality is limited to one or two sq.km.

The above observations indicate an unusual stress built up in the rocks that underlie the State. The ground cracks and anomalous fluctuation in water table are believed to be due to the response of the soft water-saturated layer under the influence of the increased stress condition. However, it was felt that much more data need to be collected to confirm this view. Monitoring the water level at close intervals of time, identification of active faults and monitoring of ground movements through GPS/differential interferometry techniques are some of the activities suggested for monitoring this phenomenon.

Seismic monitoring in Kerala State and the maintenance of a broadband station at Peechi

The broadband station at Peechi (funded by the Department of Science and Technology) was fully operational and the data was used to understand regional as well as local earthquakes. Since the project started in July 08, 2003, 9 local earthquakes have been recorded here. The most significant among these events occurred on November 08, 2003, with its source around Thalasseri (Fig. 2.3). At the time this tremor (M 3.2), the spare parts for MEQ 800 had not arrived and therefore, we could not conduct an aftershock survey. However, we used the data recorded at Peechi observatory to do a detailed study of this tremor. Parameters (location, magnitude) of this earthquake were estimated using single station data. We conducted a field study to assess the effect of this earthquake. We also examined records of tremors from various locations (Palai, Wadakkancheri, Thalasseri, Trichur etc) to study the range of travel time differences (S-P). With a good understanding of the nature of signatures from each of these locations, we are now in a position to identify the sources as soon as an event takes place. Locations are obtained later, using data from other sources. In summary, the earthquake activity in the state has generally been of a very low level during the study period. However, operation of the station has helped to identify seismic sources in the state.

The most important outcome of this project is the establishment and continued operation of an excellent station, from an azimuth that has not been previously covered, providing valuable data for a variety of studies. It is also catering to the need of monitoring local earthquakes, that occur in Kerala, although not very frequently. The observatory also serves as an excellent educational facility for professionals, students, media people and several others. The data recorded at Peechi are being cataloged and compared with the global data (NEIC) and from other available observatories. The data are being used for detailed studies of some of the regional earthquakes as well as distant events such as the September 2002, event near Port Blair, Andaman Island.

Crustal movements monitoring in Palghat Gap Region

This study aims to monitor crustal movements annually in and around the epicentral region of 1994 Wadakkancherry tremors in Palghat gap. A network of 10 GPS stations, 7 on hard rock and 3 on buildings, were monumented. Four of these at Amaiyur, Ezhumangad, Kundannur and Vellur, form the local network where as the five stations at Tirur, Attappadi, Kodungalur, Peechi and Nelliampathi serve as regional network and the one at Shornur serves as the base. The data gathered will be utilised is to monitor the baseline changes, quantify the deformation and to assess the seismogenic potential of the area. GPS survey was carried out using 3 Trimble Geodetic GPS Systems loaned from IIT, Mumbai. Data was acquired in static mode for 48 hours with 30 seconds sampling interval, during the second annual campaign in November 2003. The data processing will be carried out with Bernese GPS software available with IIT, Mumbai

Developing an improved database for seismic hazard assessment in Kerala

Detailed fieldwork was conducted in the Pala area, the epicenter of the 2000/2001 earthquakes. Landsat, thematic mapper of the area, has also been analysed and we have identified several faults in the region. Mapping of the quarries to identify sites of fractures, joints and offsets for isolating neotectonically active features was one of the major works initiated. Based on our present work, we have been able to identify the causative fault of the January 2002 earthquake near Pala, along with its geomorphic signatures. The earthquake appears to have occurred at the intersection of E-W trending and NW-SE trending faults.

GPS constraints on strain rate across the Andaman-Nicobar Islands

Third session of the Geodetic GPS campaign was carried out Andaman Niocbar Islands, during August-September 2004. New campaign mode geodetic control points were established at Little Andamans (Hutbay - HBAY) and Great Nicobar (Campbell Bay - CBAY). Total number of control points established by CESS at Andaman Islands Nicobar Islands thus comes to seven. (Diglipur - DGLP,Port Blair - PBLR, Chatam Island - CHAT, Barren Island - BRRN, Hut Bay -HBAY, Car Nicobar - CARN and Campbell Bay - BAY). This makes CESS the lone agency in India to have geodetic control points all along the Andaman -Nicobar Islands (Fig. 2.4). Initial baseline estimations for PBLR, DGLP, CARN were done last year, and processing of initial velocity estimates of these points with respect to an ideal point of reference is presently underway with GAMIT/GLOBK processing engine.

Fig. 2. 4. GPS stations in Andaman and Nicobar islands

Initial estimates of the analyzed samples show geologically recent uplift around Car Nicobar coast. Mud volcanism associated with the highly intense deformation zones at North Andamans was studied at Jawl Tikri Island. Initial estimates of the adsorbed organic gas content was computed, and comes very well within the range of other mud volcanoes of Andaman Islands.

Role of active tectonics in the development of ancient indigenous cultures around Gulf of Cambay, North West India

Extensive reconnaissance fieldwork was conducted in the coastal area bordering the Cambay basin, which mainly include Surat, Hazira, Bharuchh, Khambat, Khatana, Lothal, Motibaru and Bhavnaga. Our work consisted of local geomorphological analyses, surveying of scarps using total station and study of shallow subsurface sections by trenching and excavation. Exploratory work in shallow subsurface trenches has revealed several episodes of sandblows (seismically-induced liquefaction deposits) cross-cutting the ancient settlement levels. Most importantly, we have been able to document such features at Lothal (seat of 4000-year-old Harappan settlement) and also at Bhavnagar. Our study indicates that the Cambay rift, which like other ancient rifts in the Indian subcontinent, have the potential for moderate or large earthquakes. We have already collected sufficient amount of datable material (like charcoal, pottery shards and bones). This, together with the rich archeological database makes identification of past earthquakes easier. The information on the past events and their impact on the then existing settlements can be used for assessing the future hazard potential. Further, our study indicates that many of the sand dikes have crosscut the ancient occupation levels, particularly at Surat and Bhavnagar.