Earthquake at Bhuj, India (Filed by C.P.Rajendran)

The large earthquake that struck western India on Januray 26 (while the nation was celebrating the Republic day) is undoubtedly the worst earthquake to have hit independent India.  The rescue
operators are still struggling to clear the debris and pull out possible survivors and the country is trying to come to terms with this tragedy.
From the scientific point of view, this is not a region that has been studied extensively. In the recent years there have been some efforts to study the paleoseismicity in this region. One of the studies
that we took up is in the Rann of Kutch, to study the seismic history of the Kutch region.  Here is an abstract on our detailed paper on the deformation characteritsics in Kutch seismic zone:

Abstract of the paper by Rajendran and Rajendran ( In review, BSSA)

The 1819 earthquake in Kutch, northwestern India, is one of the most significant events to have occurred in a plate-interior setting. Despite being the second largest among the stable continental
region (SCR) earthquakes, this event has not been analyzed within the context of present-day understanding of earthquake seismology. Coseismic changes related to this earthquake include
massive ground deformation in a wide low-lying tidal-flat area. Although detailed historic accounts of this earthquake exist, many questions regarding the mode of deformation and the seismic
history of the region remain unresolved. We explored the region nearly 180 years after the earthquake, and the information gathered adds to our understanding of this event and provides a fresh
perspective on this unique intraplate seismogenic zone. A 90-km-long tract of elevated land with a peak height of 4.3 m is the most visible surface expression of this earthquake. We surveyed and
analyzed the morphological features of this scarp, and also carried out exploratory trenching in this region. The scarp morphology is suggestive of a growing fold related to a buried north dipping
thrust, rather than a discrete fault that could have resulted from a surface rupture. Extensive liquefaction field associated with the earthquake offered an ideal setting to explore the paleoearthquake
history. Age data of liquefaction features suggest that a previous event of comparable size must have occurred 800-1000 years ago. Seismic activity appears to be related to the reactivation of an
ancient rift in a stress regime that is dominated by nearly north-south compression.

Conclusions of the paper:

Our study addresses two important aspects of the 1819 Kutch earthquake- the surface deformation and the past seismicity. The results indicate that Allah Bund, a key morphological element in
this region represents a compound scarp formed by repetitive earthquakes. Overall morphological characteristics of the deformation zone suggest that the bund may represent a surface fold. A
major pre-1819 liquefaction episode has been identified in this region. The age data of sand blows supported by stratigraphic, archaeological and historical information suggest that the causative
earthquake with a magnitude comparable to the 1819 event may have occurred 800-1000 years ago.
The observations from the Kutch seismic zone may have implications on the mechanism of large SCR earthquakes like the 1811-12 New Madrid (central U.S.) and the 1886 Charleston (eastern
U.S.) that evolved from failed-rift/extensional tectonic regimes. It may now be possible to identify analogous characteristics in terms of their tectonic settings, deformation mechanisms, recurrence
periods (100s of years) and ?characteristic? sizes of earthquakes. For example, the style of surface deformation associated with the 1819 earthquake may be comparable to that of Charleston and
New Madrid events, which are characterized by arching and doming (Rhea, 1989; Müeller, et al., 1999). Studies on paleoliquefaction features suggest an average recurrence interval of about
500-600 years for Charleston and New Madrid events (Amick and Gelinas, 1991; Tuttle and Schweig, 1995). Now that we have new data from Kutch, it is worth examining whether the shared
properties of these seismic source zones can be used as inputs to recognize a single major category of SCR earthquakes, with a view to better understand their source mechanisms.
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These conclusions have bearing on Jim Zollweg?s recent  suggestions. May be these are useful to those who wish to make a comparative study of Kutch and New Madrid seismic zones.

C.P.Rajendran
 

At 12:42 PM 1/28/01 -0500, you wrote:

  Topic:  1/26/01 Indian earthquake
  Author: "Jim Zollweg" jzollweg@hotmail.com

  I want to pass along a conversation I had with Otto Nuttli around
  1973 about intraplate earthquakes.  We agreed that, short of another
  great New Madrid earthquake, one of the most interesting and
  important events that could occur would be a repeat of the 1819 Kutch
  earthquake.  Well, here we are!

  Based on the limited seismological data available to date and J. N.
  Malik's geological data, the 2001 quake may not be on the same fault
  that produced the Allah Bund in 1819 and so may not actually be a
  repeat of that event (which is comforting from a strain accumulation
  perspective).  It is nevertheless probably the largest
  instrumentally-recorded intraplate earthquake that was not associated
  with a subduction zone, making it one of the most important events of
  the instrumental era.

  Regarding its similarities to New Madrid:  Wheeler has pointed out
  some interesting ones, to which I would like to add the low
  attenuation in the Indian plate (very similar felt areas to large
  Eastern North American events).  There are also differences.  The
  1/26/01 event has a primarily reverse mechanism (Harvard CMT),
  whereas it has been presumed that most of great New Madrid events of
  1811-12 were largely strike-slip in accord with current
  microearthquake activity (the common assignment of the 1/23/1812
  event to the short dogleg of the NMSZ would suggest it was a reverse
  event).  The locale of the 1/26/01 event is much closer to the active
  collision zone of the Himalayas than New Madrid is to anything
  remotely active.  The lack of intensive geophysical exploration in
  Gujarat may at this time preclude understanding whether there is
  anything like a failed rift system in the subsurface there.

  I examined GSN seismograms from several stations, and looked at both
  Harvard's and the USGS's processing results.  I was impressed by the
  simplicity of the teleseismic P wave on the broadband stations, which
  suggests the 1/26/01 event had a simple rupture process.  This is in
  marked contrast to most large shallow events, which usually are made
  up of several prominent sub-events.  Also interestingly, it appears
  that the 1/26/01 earthquake has a large body-wave magnitude (mb)
  compared its Mw.  Those who are familiar with magnitude scaling and
  coseismic fault rupture characteristics will remember that the New
  Madrid events have very large mb magnitudes -- so large in fact that
  if the normal Ms to mb relationship held, the NMSZ would have to be
  much longer to have had enough rupture area to generate the 1811 and
  1812 earthquakes.  Here is a possible key in the Indian earthquake,
  but we need to understand what rupture process can generate such
  large mb events on relatively short fault segments.  Is it just very
  large stress drop?

  The Indian earthquake has very important implications for the nature
  of ground motion in the next major New Madrid earthquake.  Although
  there is (was?) a broadband station at Bhuj (town with >3000 killed
  on 1/26/01), the area is in general not very well covered from a
  seismic station standpoint.  I worked with a network about 200 km to
  the east in 1989, centered near the town of Kevadia.  I believe there
  was a Gujarat State seismological bureau, and that their main
  interest was in reservoir-induced seismicity.  The Bhuj station was
  part of the Indian Meteorological Department network.

  I would like to suggest that the 2001 earthquake is extremely
  important to earthquake studies in the central US.  Observations from
  this earthquake and its aftershocks may provide important constraints
  on ground motions to be expected from the next great New Madrid
  earthquakes.  If we ignore or fail to obtain data from the Indian
  earthquake sequence, it is difficult to say whether we will ever have
  another chance to constrain central/eastern US ground motion models
  at high magnitude levels prior to the next great New Madrid event.
  Things that need to be known about the Indian event are:
  source mechanism
  time history of main shock rupture
  stress drop of main shock and aftershocks
  aftershock patterns in space and time, and their long-term decay
  near-field ground motion
  aftershock ground motion
  local and regional attenuation
  geology and structure of the source area
  scarp characteristics, if surface rupture occurred (probable)
  liquefaction features, if they occurred (probable)
  paleoseismology of area faults

  I have an 11-station portable telemetry network available, as well as
  6 broadband digital seismographs currently in house.  I suggest that
  those who might be interested in a multi-disciplinary,
  multi-institution effort to study the Indian earthquake as a possible
  analog to New Madrid organize a science plan.  There are some
  complications to working in Gujarat:  proximity to the Pakistan
  border, difficulty (even in normal times) of travelling from place to
  place, Indian sensitivity to outsiders, climate, etc.  My work there
  in 1989 was not easy.  I believe it will be necessary to arrange to
  be hosted by an Indian institution if a field program is to have any
  chance of success.  Despite the difficulties, I think it important to
  forge ahead due to the potential value of the results.

  Jim Zollweg
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