Isoseismals for the Kutch earthquake of 26th January 2001
A Sinvhal1, P R Bose2, V Prakash1, A Bose3, A K Saraf4 and H Sinvhal4
1Department of Earthquake Engineering, Indian Institute of Technology,
Roorkee, 247 667, India
2Department of Civil Engineering, Delhi College of Engineering, Bawana
Road, Delhi 110 042, India
3Designers and Planners Combine, AG 57, Shalimar Bagh, Delhi, 110 052,
India
4Department of Earth Sciences, Indian Institute of Technology, Roorkee,
247 667, India
Damage observed during the Kutch earthquake of 26th January 2001 is classified
according to the type of structure. This damage pattern has been used to
draw the isoseismal map on the basis of the intensity scale given in IS
1893{2002 which covers only traditional one to two storey houses. Having
thus estimated intensities, and observed damage to other types of structures,
a new criterion was adopted which is included in this paper. Areas that showed
maximum damage to structures have been assigned maximum intensity X.
A simulation of earthquake induced undrained pore pressure changes
with bearing on some soil liquefaction observations following the 2001 Bhuj
earthquake
Irene Sarkar1 and Ramesh Chander2
1Department of Earth Sciences, Indian Institute of Technology, Roorkee
247 667, India
2House no. 290, Sector 4, Mansa Devi Complex, Panchkula 134 109, India
The Bhuj earthquake of January 26th, 2001, induced wide spread liquefaction
within the Kachch peninsula. It has been pointed out that inundation due
to soil liquefaction was short lived in some parts than in others in the
affected region. Several geological, seismological and hydrological factors
would have cumulatively contributed to these observed changes.
We simulate in this article, undrained or short-term change in pore pressure
in a poroelastic half space, in response to a simplified model of the Bhuj
earthquake source. We find that the regions of relatively shorter lived inundation
due to soil liquefaction may fall in the region where pore pressure responsible
for soil liquefaction attributable to strong ground shaking was counteracted
by pore pressure changes due to undrained poroelastic effect and vice versa.
Statistical parameters of Bhuj earthquake sequence of January 26th,
2001
M A Shaik and Sanjay Srivastava
Seismology Unit, Engineering Geology Division, Gujarat Engineering
Research Institute, Race Course, Vadodara 390 007
An intraplate earthquake of magnitude (Mc) 6.9 (Anon
2001a) struck Bhuj and the adjoining region of Kachchh in Gujarat on January
26th, 2001 at about 0316 hrs (GMT) and was followed by a number of aftershocks.
The epicentre of this earthquake was located at 23.4N and 70.28E
close to the Kachchh mainland fault. The intensity observed around the epicenter
was X on the MSK scale. A study of 531 aftershocks, in the magnitude range
of 3.0{5.7, recorded at Vadodara Seismological Observatory till March 31st,
2001 has been carried out and various statistical parameters calculated.
The total energy released during the study period is calculated to be 8:2
1014 joule. Sudden occurrence of the main shock without any foreshock
in the same tectonic system is a unique feature of this sequence. The b-value
(0.86), value of M0{M1 (1.2), high M1=M0 (0.89) and high value of the decay
constant h (0.91), all support the tectonic origin of the present study.
An eyewitness account of the Bhuj earthquake
M K Gupta
India Meteorological Department, Pune 411 005, India.
The occurrence of a severe earthquake is a rare event with its effect localized
in a limited region. There are no prior indications of its occurrence too;
hence experiencing such an event is just a matter of chance, which the author
had by virtue of his posting at Bhuj. This paper presents a detailed account
of observations made in the wake of the Bhuj earthquake of January 26th
2001, describing physical and mental reactions during the earthquake, the
post-quake scenario, the nature and cause of damage to buildings, the trend
of aftershocks, various deformities, including ruptures and fissures on the
surface of the earth, etc. which may be useful for a detailed study of the
seismological activity in the region.
Numerical simulation of liquefaction behaviour of granular materials
using Discrete Element Method
T G Sitharam1 and S V Dinesh2
1Associate Professor, Department of Civil Engineering, Indian Institute
of Science, Bangalore 560 012, India.
2Research Scholar, Department of Civil Engineering, Indian Institute of
Science, Bangalore 560 012, India.
In this paper, numerical simulation of 3-dimensional assemblies of 1000
polydisperse sphere parti
cles using Discrete Element Method (DEM) is used to study the liquefaction
behaviour of granular materials. Numerical simulations of cyclic triaxial
shear tests under undrained conditions are performed at different confining
pressures under constant strain amplitude. Results obtained in these numerical
simulations indicate that with increase in confining pressure there is an
increase in liquefaction resistance.
Behaviour of masonry structures during the Bhuj earthquake of January
2001
K S Jagadish1, S Raghunath2 and K S Nanjunda Rao3
1Professor, Department of Civil Engineering, Indian Institute of Science,
Bangalore 560 012, India
2Lecturer, Department of Civil Engineering, B.M.S College of Engineering,
Bangalore 560 019, India
3Senior Scientific Officer, Department of Civil Engineering, Indian Institute
of Science, Bangalore 560 012, India
A variety of masonry structures suffered damage during the recent Bhuj
earthquake. Some of the traditional masonry structures had no earthquake
resistant features and suffered considerable damage. This paper attempts
to evaluate the behaviour of masonry structures based on the type of masonry
used in places like Bhuj, Anjar, Bhachau, Morbi, Samakhyali and several
other places. Quite a few masonry buildings had used earthquake resistant
features like lintel bands and corner reinforcements. The cracking and failure
patterns of such buildings have also been examined. The paper concludes
with a discussion on the relevance of the current codal provisions for earthquake
resistance of masonry structures and the direction of further research in
the area.
2.5D Simulation of basin-edge effects on the ground motion characteristics
J P Narayan
Department of Earthquake Engineering, Indian Institute of Technology,
Roorkee 247 667, India.
The effects of basin-edge and soil velocity on the ground motion characteristics
have been simulated using 2.5D modeling. One of the most significant advantages
of the 2.5D simulation is that 3D radiation pattern can be generated in
a 2D numerical grid using double-couple shear dislocation source. Further,
2.5D numerical modeling avoids the extensive computational cost of 3D modeling.
The responses of basin-edge model using di erent soil velocities revealed
that surface waves were generated near the edge of the basin and propagated
normal to the edge, towards the basin. Further, the results depict increase
of ampli cation, duration and surface wave generation with the decrease
in soil velocity.
Performance of elevated tanks in Mw 7.7 Bhuj earthquake of January
26th, 2001
Durgesh C Rai
Department of Civil Engineering, Indian Institute of Technology, Kanpur
208 016, India.
The current designs of supporting structures of elevated water tanks are
extremely vulnerable under lateral forces due to an earthquake and the Bhuj
earthquake provided another illustration when a great many water tank stagings
suffered damage and a few collapsed. The more popular shaft type stagings
suffer from poor ductility of thin shell sections besides low redundancy
and toughness whereas framed stagings consist of weak members and poor brace-column
joints. A strength analysis of a few damaged shaft type stagings clearly
shows that all of them either met or exceeded the strength requirements of
IS:1893{1984, however, they were all found deficient when compared with requirements
of the International Building Code. IS:1893{1984 is unjustifiably low for
these systems which do not have the advantage of ductility and redundancy
and are currently being underestimated at least by a factor of 3 and need
an upward revision of forces immediately.
Study of the epicentral trends and depth sections for aftershocks
of the 26th January 2001, Bhuj earthquake in western India
S G Gaonkar1, B V Srirama1, S R Samaddar1, D V Punekar1, Sagina
Ram2, Reena De3 and J R Kayal4
1Geological Survey of India(CR), Seminary Hills, Nagpur, 440 006, India.
2Geological Survey of India(NR), Sector E, Aligunj, Lucknow, India.
3Geological Survey of India(ER), Karunamayee, Salt Lake, Kolkata, India.
4Geological Survey of India(CGD), 27 J.N. Road, Kolkata, 700 016, India.
The Geological Survey of India (GSI) established a twelve-station temporary
microearthquake (MEQ) network to monitor the aftershocks in the epicenter
area of the Bhuj earthquake (Mw7:5) of 26th January 2001. The main shock
occurred in the Kutch rift basin with the epicenter to the north of Bhachao
village, at an estimated depth of 25km (IMD). About 3000 aftershocks (Md
1:0), were recorded by the GSI network over a monitoring period of about
two and half months from 29th January 2001 to 15th April 2001. About
800 aftershocks (Md 2:0) are located in this study.
The epicenters are clustered in an area 60km 30 km, between 23:3N and
23:6N and 70E and 70:6E. The main shock epicenter is also located within
this zone.
Two major aftershock trends are observed; one in the NE direction and other
in the NW direction. Out of these two trends, the NE trend was more pronounced
with depth. The major NE-SW trend is parallel to the Anjar-Rapar lineament.
The other trend along NW-SE is parallel to the Bhachao lineament. The aftershocks
at a shallower depth (< 10 km) are aligned only along the NW-SE direction.
The depth slice at 10km to 20km shows both the NE-SW trend and the NW-SE
trend. At greater depth (20 km{38 km) the NE-SW trend becomes more predominant.
This observation suggests that the major rupture of the main shock took place
at a depth level more than 20 km; it propagated along the NE-SW direction,
and a conjugate rupture followed the NW-SE direction. A N-S depth section
of the aftershocks shows that some aftershocks are clustered at shallower
depth 10 km, but intense activity is observed at 15{38km depth. There is
almost an aseismic layer at 10{15km depth. The activity is sparse below 38
km. The estimated depth of the main shock at 25km is consistent with the
cluster of maximum number of the aftershocks at 20{38 km. A NW-SE depth section
of the aftershocks, perpendicular to the major NE-SW trend, indicates a SE
dipping plane and a NE-SW depth section across the NW-SE trend shows a SW
dipping plane. The epicentral map of the stronger aftershocks M 4:0 shows
a prominent NE trend. Stronger aftershocks have followed the major rupture
trend of the main shock. The depth section of these stronger aftershocks
reveals that it occurred in the depth range of 20 to 38 km, and corroborates
with a south dipping seismogenic plane.
Estimation of S-wave site response in and around Delhi region
from weak motion data
S K Nath1, P Sengupta1, S K Srivastav2, S N Bhattacharya2, R S Dattatrayam2,
R Prakash2 and H V Gupta2
1Department of Geology and Geophysics, Indian Institute of Technology,
Kharagpur 721 302, India
2India Meteorological Department, New Delhi 110 003, India
e-mail: nath@gg.iitkgp.ernet.in
Site response in and around Delhi is studied using digital seismograms recorded
by a thirteen-
station VSAT-based 24-bit digital Delhi telemetry network of the India Meteorological
Department. Nine local (Ml 2:3) and nine regional (Ml 3:9) earthquakes
are selected for the estimation of site amplification factor using the classical
standard spectral ratio for regional events (Ridge Delhi Observatory being
the reference station), normalized standard spectral ratio for local events,
horizontal-to-vertical spectral ratio or receiver function and the generalized
inversion techniques in the frequency range of 0.5 to 7.5 Hz. Site response
curves at all the thirteen stations exhibit station to station variation
of the site amplification factor reflecting the changes in geologic/geotectonic/soil
conditions. A comparison of the site response values obtained by the generalized
inversion with those computed using receiver function technique shows a large
scatter even though the pattern of the curves remain more or less similar.
However, the site effects computed by generalized inversion and standard
spectral ratio exhibit a good 1:1 correspondence. The peaks yielded by all
the methods have been observed to occur at the same frequencies. It is evident
that the softer fluvial deposits of the newer alluvium of the east Yamuna
sector show steeper site amplification gradient at lower frequencies, while
the greater Delhi experiences moderate site amplification. The variation
of site response corroborates the abrupt changes in intensity from one location
to another due to local site condition.
Aftershock activity of Bhuj earthquake of January 26th, 2001
Ashwani Kumar, S C Gupta, A K Jindal, Sanjay Jain and Vandana
Department of Earthquake Engineering, Indian Institute of Technology
Roorkee, Roorkee 247 667, India
Following a large-sized Bhuj earthquake (Ms = 7:6) of January 26th, 2001,
a small aperture 4- station temporary local network was deployed, in the
epicentral area, for a period of about three weeks and resulted in the recording
of more than 1800 aftershocks (−0:07 ML < 5:0). Prelimi-
nary locations of epicenters of 297 aftershocks (2:0 ML < 5:0) have
brought out a dense cluster of aftershock activity, the center of which falls
20km NW of Bhachau. Epicentral locations of after-shocks encompass a surface
area of about 5040km2 that seems to indicate the surface projection of the
rupture area associated with the earthquake. The distribution of aftershock
activity above magnitude 3, shows that aftershocks are nonuniformly distributed
and are aligned in the north, northwest and northeast directions. The epicenter
of the mainshock falls on the southern edge of the delineated zone of aftershock
activity and the maximum clustering of activity occurs in close proximity
of the mainshock. Well-constrained focal depths of 122 aftershocks show that
89% of the aftershocks occurred at depths ranging between 6 and 25km and
only 7% and 4% aftershocks occur at depths less than 5 and more than 25km
respectively. The Gutenberg-Richter (GR) rela- tionship, log N = 4:52−0:89ML,
is tted to the aftershock data (1:0 ML < 5:0) and the b-value of 0.89
has been estimated for the aftershock activity.
Aftershocks of 26th January 2001 Bhuj earthquake and seismotectonics
of the Kutch region
K S Misra, R Bhutani and R Sonp
Geological Survey of India, Alandi Road, Pune - 6, India
email: gsi−pune@vsnl.com
The 26th January 2001 Bhuj earthquake was followed by intense aftershock
activity. Aftershock data from United States Geological Survey (USGS) utilized
in this study encompasses three months period from 26th January to 26th April
2001. Epicenters of the aftershock are plotted on a map depicting active
faults. All the aftershocks of magnitude > 5 and 70% of those ranging
between magnitude 3 and 5 are confined to an area resembling a horseshoe pattern
with a pointed end towards NE. The other 20% of magnitude 3 to 5 are enclosed
within an almost parallel boundary. Only 10% are found to be beyond this
limiting boundary. 50% of the recorded aftershocks took place within the
first week of the main event and this study reveals that the basic characteristic
pattern of aftershock activity can be determined on the basis of the data
of only one week.
Four major NW-SE trending active faults are mapped in the Kutch region.
They define the western limit of Cambay structure and also mark the western
limit of Dharangadhra and Wadhwan basins along the SE continuation in Saurashtra.
These faults separate the Kutch region into two geologically different blocks.
On the SW side the mapped horseshoe pattern gets characteristically truncated
along the western most fault, which is characterized by a strike-slip movement
in the south and vertical movement in the north. The present study has revealed
that the epicenter of the 26th January earthquake is located in the vicinity
of the Bhachau township, close to the intersection with the Kutch mainland
fault. Furthermore, it has been noticed that most of the epicenters of the
aftershock are confined in the intersectional area of the Kutch mainland fault
and the NW-SE faults.
Fault plane solutions of the January 26th, 2001 Bhuj earthquake
sequence
Reena De1, S G Gaonkar2, B V Srirama2, Sagina Ram3 and J R Kayal4
1Geological Survey of India, Eastern Region, Salt Lake, Calcutta 700
091, India.
2Geological Survey of India, Central Region, Nagpur 440 006, India.
3Geological Survey of India, Northern Region, Lucknow 226 024, India.
4Geological Survey of India, 27, J. L. Nehru Road, Calcutta 700 016, India.
e-mail: jr−kayal@hotmail.com
A 12-station temporary microearthquake network was established by the Geological
Survey of India for aftershock monitoring of the January 26th, 2001 Bhuj
earthquake (MW 7.6) in the Kutch district of Gujarat state, western India.
The epicentres of the aftershocks show two major trends: one in the NE direction
and the other in the NW direction. Fault-plane solutions of the best- located
and selected cluster of events that occurred along the NE trend, at a depth
of 15{38 km, show reverse faulting with a large left-lateral strike-slip
motion, which are comparable with the main-shock solution. The NW trending
upper crustal aftershocks at depth < 10 km, on the other hand, show reverse
faulting with right-lateral strike-slip motion, and the mid crustal and lower
crustal aftershocks, at a depth of 15{38 km, show pure reverse faulting as
well as reverse faulting with right-lateral and left-lateral strike-slip
motions; these solutions are not comparable with the main-shock solution.
It is inferred that the intersection of two faults has been the source area
for stress concentration to generate the main shock and the aftershocks.
A media-based assessment of damage and ground motions from the January
26th, 2001 M 7.6 Bhuj, India earthquake
Susan E Hough1, Stacey Martin2, Roger Bilham3 and Gail M Atkinson4
1United States Geological Survey, Pasadena, California.
2Nowrosjee Wadia College, Pune, India.
3University of Colorado, Boulder, Colorado.
4Ottawa, Canada.
We compiled available news and internet accounts of damage and other effects
from the 26th January, 2001, Bhuj earthquake, and interpreted them to obtain
modified Mercalli intensities at over 200 locations throughout the Indian
subcontinent. These values are used to map the intensity distribution using
a simple mathematical interpolation method. The maps reveal several interesting
features. Within the Kachchh region, the most heavily damaged villages are
concentrated towards the western edge of the inferred fault, consistent with
western directivity. Significant sediment- induced amplification is also
suggested at a number of locations around the Gulf of Kachchh to the south
of the epicenter. Away from the Kachchh region intensities were clearly amplified
significantly in areas that are along rivers, within deltas, or on coastal
alluvium such as mud flats and salt pans. In addition we use fault rupture
parameters inferred from teleseismic data to predict shaking intensity at
distances of 0{1000 km. We then convert the predicted hard rock ground motion
parameters to MMI using a relationship (derived from internet-based intensity
surveys) that assigns MMI based on the average e ects in a region. The predicted
MMIs are typically lower by 1{2 units than those estimated from news accounts.
This discrepancy is generally consistent with the expected effect of sediment
response, but it could also reflect other factors such as a tendency for
media accounts to focus on the most dramatic damage, rather than the average
effects. Our modeling results also suggest, however, that the Bhuj earthquake
generated more high-frequency shaking than is expected for earthquakes of
similar magnitude in California, and may therefore have been especially damaging.
Flexure of the Indian plate and intraplate earthquakes
Roger Bilham, Rebecca Bendick and Kali Wallace
CIRES and Department of Geological Sciences, University of Colorado, Boulder
CO 80309-0399.
The flexural bulge in central India resulting from India's collision with
Tibet has a wavelength of approximately 670 km. It is manifest topographically
and in the free-air gravity anomaly and the geoid. Calculations of the stress
distribution within a flexed Indian plate reveal spatial variations throughout
the depth of the plate and also a function of distance from the Himalaya.
The wave- length (and therefore local gradient) of stress variation is a
function of the effective elastic thickness of the plate, estimates of which
have been proposed to lie in the range 40{120 km. The imposition of this
stress field on the northward moving Indian plate appears fundamental to
explaining the current distribution of intraplate earthquakes and their mechanisms.
The current study highlights an outer trough south of the flexural bulge
in central India where surface stresses are double the contiguous compressional
stresses to the north and south. The Bhuj, Latur and Koyna earthquakes and
numerous other recent reverse faulting events occurred in this compressional
setting. The N/S spatial gradient of stress exceeds 2 bars/km near the flexural
bulge. The overall flexural stress distribution provides a physical basis
for earthquake hazard mapping and suggests that areas of central India where
no historic earthquakes are recorded may yet be the locus of future damaging
events.
Pre-seismic, co-seismic and post-seismic displacements associated
with the Bhuj 2001 earthquake derived from recent and historic geodetic data
Sridevi Jade1, M Mukul1, I A Parvez1, M B Ananda1, P D Kumar1, V K Gaur1,
R Bendick2, R Bilham2, F Blume2, K Wallace2, I A Abbasi3, M Asif Khan3 and
S Ulhadi3
1CSIR Centre for Mathematical Modelling and Computer Simulation, Bangalore
560 037, India
2CIRES & Department of Geol. Sci., Univ. of Colorado, Boulder, CO 80309-0399,
USA
3University of Peshawar, Peshawar 25 120, Pakistan
The 26th January 2001 Bhuj earthquake occurred in the Kachchh Rift Basin
which has a long his
tory of major earthquakes. Great Triangulation Survey points (GTS) were
rst installed in the area in 1856{60 and some of these were measured using
Global Positioning System (GPS) in the months of February and July 2001.
Despite uncertainties associated with repairs and possible reconstruction
of points in the past century, the re-measurements reveal pre-seismic, co-seismic
and post-seismic deformation related to Bhuj earthquake. More than 25 -strain
contraction north of the epicenter appears to have occurred in the past 140
years corresponding to a linear convergence rate of approximately 10 mm/yr
across the Rann of Kachchh. Motion of a single point at Jamnagar 150km south
of the epicenter in the 4 years prior to the earthquake, and GTS-GPS displacements
in Kathiawar suggests that pre-seismic strain south of the epicenter was
small and differs insignificantly from that measured elsewhere in India.
Of the 20 points measured within 150km of the epicenter, 12 were made at
existing GTS points which revealed epicentral displacements of up to 1m,
and strain changes exceeding 30 -strain. Observed displacements are consistent
with reverse co-seismic slip. Re-measurements in July 2001 of one GTS point
(Hathria) and eight new points established in February reveal post-seismic
deformation consistent with continued slip on the Bhuj rupture zone.