2001 Bhuj Earthquake

1
2001 Bhuj Earthquake

• Meredith A. Langstaff

2
Earthquake Basics

• MW 7.6 on Jan. 26, 2001 in the Indian state
  Gujarat
• gt 20,000 killed
• 150,000 injured
• 1 million homes destroyed
• 10 billion in damage
• Numerous reports of liquefaction and sand blows
• gt 4000 aftershocks

Source Rastogi (2004)
3
Tectonic Setting

• Convergence to North
• Bhuj considered an intraplate earthquake
• Known as a seismically active region
• Last large earthquake the 1819 Allah Bund
  earthquake, thought to be same size as 2001 event
• Perhaps best analog for New Madrid Seismic Zone

Source Antolik and Dreger (2003)
4
Regional Instrumentation

• No regional seismic or GPS networks at time of
  rupture
• No strong ground motion records at site of
  earthquake
• Multiple teams set up temporary networks in the
  weeks to month after the mainshock
• Most studies analyze the aftershocks

Source Mandal et al. (2004)
5
Causative Fault

• Numerous aftershock studies (Mandal et al. 2004
  Bodin et al., 2004) confirm an E-W trending blind
  thrust dipping 45 degrees to South
• Depth 10-45 km
• Reactivation of failed rift from Gondwana
• Reactivated 40 mya as a result of collision with
  Asia
• Anomalously high stress drop 20MPa

Source Bodin and Horton (2004)
6
Observed Ground Motions

• Hough et al. (2002) compiled personal and media
  reports of damage
• Assigned Modified Mercali Intensities (MMIs) at
  locations
• Create intensity distribution from a
  continuous-curvature gridding algorithm
• Heaviest damage to West of fault
• Finite-fault source model for ground motions
  under-predicts data
• Media bias? Building vulnerability? Nature of
  shaking for intraplate earthquakes?

Hough et al. (2002)
7
Slip Distribution

• Antolik and Dreger (2003) used finite fault slip
  inversion to find slip distribution
• Most slip occurs close to hypocenter
• Few aftershocks in hypocenter region
• Preferred model limits slip at surface
• Primary rupture upwards and to northwest
• Second region of slip in shallower part of fault,
  west of hypocenter.
• West component of directivity to match ground
  motions?

Antolik and Dreger (2003)
8
Aftershock Studies

• Aftershocks observed to depths gt 30km
• Bimodal distribution peaks at 26km and 10km
• Bodin and Horton (2004) argue aftershocks are
  consistent with deep slip during the mainshock
• Reflect bimodal depth dependent brittles-strength
  profile for thrust faulting?
• Other interpretation lack of aftershocks in
  region of mainshock
• Several authors report high Vp region surrounding
  mainshock - volcanic intrusion from rifting?

Source Bodin and Horton (2004)
9
Fluid-Driven Earthquake?

• Kayal et al. (2002) and Mishra and Zhao (2003)
  report estimates of crack density (?), saturation
  rate (?), porosity (?), and Poissons ratio (?)
  from Vp and Vs aftershock measurements
• Hypocenter located in region of high Vp, low Vs,
  and high- ?, high- ?, high- ?, and high- ?
• Infer fluid-filled, fractured rock matrix

Source Mishra and Zhao (2003)
10
Analog for New Madrid?

• Bodin et al. (2004) aftershock study finds
  similar ground motion attenuation
• New study (Miao and Langston, 2008) finds India
  more similar to Southern California

Source Bodin et al. (2004)
Source Miao and Langston (2009)
11
Diffuse Plate Boundary Theory

• Some argue only 400km from plate boundary
• In US terms, the location of Nevada
• Seismicity may be a product of diffuse plate
  boundary
• Stein et al. propose formation of Sind Block
  microplate
• High stress drops associated with intraplate
  earthquakes
• Slip orientation consistent with compressional
  stresses from Indian plate collision

12
A Note on Geology

• Although didnt rupture surface, several surface
  features have been mapped
• Sand blow craters may include records of past
  seismicity

Source Rajendran et al. (2001)
Source Rajendran et al. (2002)
13
Conclusions

• Possible intraplate earthquake may be an analog
  for other continental seismicity
• Two regions of slip one at depth and one closer
  to surface
• Bimodal distribution of aftershocks may indicate
  deep slip during mainshock
• Calculations from Vp and Vs measurements suggest
  fluid-filled, fractured rock matrix
• Not everybody agrees! Interplate/Intraplate?
  Analog for New Madrid?

14
References

1. Antolik, M. and D. S. Dreger (2003). Rupture
   process of the 26 January 2001 MW 7.6 Bhuj,
   India, earthquake from teleseismic broadband
   data. Bull. Seism. Soc. Am. 93 (3), 1235-1248.
   
2. Bodin, P. and S. Horton (2004). Source parameters
   and tectonic implications of aftershocks of the
   MW 7.6 Bhuj earthquake of 26 January 2001. Bull.
   Seism. Soc. Am. 94 (3), 818-827.
3. Bodin, P., L. Malagnini, A. Akinci (2004).
   Ground-motion scaling in the Kachchh Basin,
   India, deduced from aftershocks of the 2001 MW
   7.6 Bhuj earthquake. Bull. Seism. Soc. Am. 94
   (5), 1658-1669.
4. Hough, S. E., S. Martin, R. Bilham, and G. M.
   Atkinson (2002). The 26 January 2001 M 7.6 Bhuj,
   India, earthquake observed and predicted ground
   motions. Bull. Seism. Soc. Am. 92 (6),
   2061-2079.
5. Kayal, J. R., D. Zhao, O. P. Mishra, R. De, and
   O. P. Singh (2002). The 2001 Bhuj earthquake
   tomographic evidence for fluids at the hypocenter
   and its implications for rupture nucleation. Geo.
   Res. Let. 29 (24), doi 10.1029/2002GL015177
6. Mandal, P., B. K. Rastogi, H. V. S. Satyanaraya,
   M. Kousalya, R. Vijayraghavan, C. Satyamurty, I.
   P. Raju, A. N. S. Sarma, and N. Kumar (2004).
   Characterization of the causative fault system
   for the 2001 Bhuj earthquake of MW 7.7.
   Tectonophys.378, 10
7. Miao, Q. and C. A. Langston (2008). Comparative
   study of distance attenuation in the Central
   United States and Western India. Eastern Section
   Seismological Research Letters, 79 (3),
   446-456.
8. Mishra, O. P. and D. Zhao (2003). Crack denstiy,
   saturation rate and porosity at the 2001 Bhuj,
   India, earthquake hypocenter a fluid -driven
   earthquake? Earth Pl. Sci. Let. 212, 393-405.
9. Rajendran K., C. P. Rajendran, M. Thakkar, and M.
   P. Tuttle (2001) The 2001 Kutch (Bhuj)
   earthquake coseismic surface features and their
   significance. Cur. Sci. 80 (11), 1397-1405.
10. Rajendran, K., C. P. Rajendran, M. Thakkar, and
    R. K. Gartia (2002) Sand blows from the 2001 Bhuj
    earthquake reveal clues on past seismicity. Cur.
    Sci. 83 (5), 603-610.