Detection of Bhuj Earthquake Liquifaction

Christopher A. McGee

December 6, 2005

ES771XA-Remote Sensing

Table of Contents

Abstract

The purpose of this research is to demonstrate the value of utilizing remote sensing for the detection of earthquake-induced liquifaction. The subject event occurred on 26 January 2001 near the village of Bhuj in the state of Gujarat, India.

Landsat 7 ETM+ imagery was obtained, courtesy of the University of North Alabama's Department of Geography, of the affected region. This imagery was acquired prior to the event, on 8 January 2001, and two weeks after, on 9 February 2001. Research of various professional and educational websites provided information relating to the geography and geology of the affected area, as well as tectonic setting, seismic history, location and characteristics of the earthquake, liquifaction, damage, and casualty data.

These data were combined with image analysis, courtesy of the University of North Alabama (UNA) to gain an understanding of the liquifaction phenomenon resulting from the Bhuj event. Various band combinations were utilized to determine the best combination for revealing soil moisture content, and to allow ease of discerning the presence and effects of liquifaction. Histogram analysis was performed on all nine ETM+ bands to reveal reflectance changes between 8 January and 9 February, 2001.

The 8,4,3 combination was selected due to its ability to penetrate the Earth's atmosphere, clearly show shorelines and coasts, and to reveal moisture and texture characteristics of soils. Using the 8,4,3 band combination, the 9 February 2001 image clearly shows increased soil moisture, streams, and areas of runoff which did not exist on 8 January 2001. Histogram analysis indicates reflectance changes consistent with moisture increases as near-infrared and mid-infrared reflectance is lower in the post-earthquake image. This study concludes that ETM+ imagery provides an effective tool for determining and demonstrating liquifaction of soil after a seismic event.

Back to Top

References

Back to Top

Geography and Geology

The village of Bhuj lies in the Kachchh region of the state of Gujarat in western India. The region is relatively populated as the towns and villages of Anjhaar, Bhachau, and Vondh are located within its boundaries. Eastward-trending faults and folds characterize Mesozoic, Tertiary, and Quaternary geologic units, the most significant of this study being the Kachchh Mainland fault. Anticlines and salt domes from the folding of Quaternary fluvial structures form the northern portion of the region, and folded and thrusted Quaternary units make up the southern Kachchh geology. The Kachchh Mainland fault possesses an orientation of N60E,65S with a slip trend of 62 (EERI, 2001)

Back to Top

Tectonic Setting

According to the Earthquake Engineering Research Institute (EERI), the Indian tectonic plate migrates toward the north at a rate of 55 to 60 millimeters per year; likewise, the Asian plate is moving in the same direction at 25 to 30 millimeters per year. The difference in speed is responsible for the formation of the Himalayan Mountains and the 20 to 25 millimeter-per-year outward forcing of crustal blocks along the subcontinent's border with Pakistan. South of the plate margin, motion is a mere 1-5 millimeters per year. This array of motion speed and direction creates one of the most seismically active regions in the world, and has been responsible for a number of major and minor earthquakes, including the 26 January 2001 magnitude 7.7 Bhuj event. The state of Gujarat sits atop a zone marking the transition from active plate movement to a more stable continental land mass (EERI, 2001).

Back to Top

Seismic History

A new chapter in India's seismic history was recorded on 26 January 2001 when a magnitude 7.7 earthquake struck the state of Gujarat. An estimated 16 million people were affected in some way by the death and destruction inflicted. A similar event occurred in 1819 which also measured magnitude 7.7 and formed Lake Sindri, a 6-meter depression which fills during summer monsoons. Since the 1819 event, 6 other earthquakes have damaged the region, although not to the extent of the 1819 and 2001 events. Due to much lower population density in 1819, approximately 2,000 fatalities occurred; the 2001 earthquake is estimated to have killed over 20,000 people. However, the percentages of deaths to total population are quite similar (Colorado, 2001).

Back to Top

Earthquake Location

The earthquake striking the Kachchh region of Gujarat, India, on 26 January 2001 was centered approximately 800 kilometers southwest of Delhi in the western portion of the country. The epicenter was near the remote Little Rann of Kutch, but within 150 to 200 kilometers of several villages and towns. The proximity to populated areas, coupled with a shallow 17-kilometer focus, resulted in massive destruction and fatalities. The area is mainly barren, with the exception of a belt of arable land stretching along the shore of the Gulf of Kachchh. The affected area also experienced magnitude 5.0 to 5.8 aftershocks for several days subsequent to the main earthquake (Seismo-watch, 2001).

Back to Top

Earthquake Characteristics

The Bhuj earthquake had a focus approximately 17 kilometers in depth and caused maximum uplift of approximately 2 meters near the epicenter. Reports state that 2 pulses account for about 85 seconds of strong shaking, followed by several minutes of moderate shaking. Deformation of alluvial units along the Mainland fault's northern edge, due to extensional and compressional movement, resulted in ground surface faulting, sand boils, and surface bulging due to compression (EERI, 2001).

Back to Top

Detecting Liquifaction

As extensional and compressional movements occur, ground water is forced upward due to compaction of water-containing subsurface structures. In the areas of the Banni Plains, the Great Rann, the Gulf of Kachchh, Kandla River, and Little Rann, soil characteristics and topography cause a high probability of liquefaction during seismic events (EERI, 2001). Soil compaction was so great during the 2001 event that some desert rivers flowed after over 100 years of remaining dry. In Kachchh, mud volcanoes were found, some of which were hundreds of meters in diameter. In the southern Rann, one such feature covers a 5-kilometer area with mud and sand. Groundwater level has risen and new springs have been found around the affected area, the result of topographical changes. Pumping groundwater from the area takes approximately a third less time for water to reach the surface due to higher water table levels, and in some locations, saline springs have been discovered. The desert area of western Kutch now has water flowing as the Sindhu River's course altered, another result of the earthquake, and water table depths of 10 to 15 feet have been reported around the Khari River and the Large Rann of Kutch. Prior to the 2001 earthquake, this drought-ridden area suffered from annual water crises since the 1819 earthquake changed the course of the Sindhu River away from the region (Colorado, 2001).

Back to Top

Processed Landsat-7 ETM+ Imagery

Courtesy of UNA

Histogram analysis of ETM+ band values indicated a moisture increase in the 9 February 2001 images compared to the 8 January 2001 set. Particularly, the red band showed an increase in mean value from 47 to 53, as sediment-laden surface water and additional soil moisture reflect more red wavelengths of the spectrum. Band 5 mid-infrared reflectance decreased from a value of 64 in the before-event image, to 48 in the post-earthquake image. The addition of soil moisture and surface water resulted in higher absorption of mid-infrared wavelengths, reducing the amount of band 5 MIR sensed by Landsat 7. Band 7 MIR is effective in revealing areas of hydrothermal alteration in rock features. Mean values of band 7 between the pre- and post-earthquake images increased from 111 to 132, which supports reports of "steaming hot water and lava coming out of the other areas of the quake devastated area" (Colorado, 2001).

Back to Top

Band Combination 7,5,3

Band Combination 7,5,3 mid-infrared reflectance shows well-defined soil and rock boundaries and red reflectance indicates a difference in sediment-laden water between the 8 January and 9 February 2001 images. More soil moisture is evident in the latter image, as are new drainage patterns.

Back to Top

Band Combination 4,5,1

Band Combination 4,5,1 clearly defines land and water boundaries, and the after-event image indicates the presence of more water in the soil, as well as more surface drainage.

Back to Top

Band Combination 7,5,4

Band Combination 7,5,4 also shows new drainage patterns in the February image, as well as increased soil moisture from liquifaction.

Back to Top

Band Combination 8,4,3

Band Combination 8,4,3 gives the best display of post-earthquake change. These two images using the 8,4,3 band combination, with ETM+'s 15-meter resolution panchromatic band, near-infrared and red reflectance give sharp land/water boundaries, showing clearly how new drainage patterns developed, a large increase in soil moisture as darker blue in the first image due to greater near-infrared absorption, and more red in the second resulting from a greater amount of soil moisture, in addition to dark blues inland of the coastline as liquifaction created new surface water features not present in the earlier image.

Back to Top

Damage and Casualties

The 26 January 2001 earthquake in Gujarat was the most devastating seismic event to affect the state since the last magnitude 7.7 event in 1819. More than 20,000 people died and over 167,000 injuries were reported. Both rail and highway traffic into and out of the entire Kachchh region was completely cut off for two days. Numerous bridges, dams, and ports were destroyed or severely damaged as a result of liquifaction of the blue marine clay soil on which they are constucted. Approximately 1,000,000 homes were destroyed or seriously damaged, as were many commercial, industrial, and public utility facilities. Total blackout resulted in several towns and villages; communications in Bhuj were disrupted for two days when fiber optic cables were damaged, and water supplies were affected as liquifaction caused some wells to become turbid and others tested positive for metal contaminants and anaerobic sludge (EERI, 2001)

Back to Top