the 2003 bam, iran earthquake: what we knew, what we didn’t know and what we expect in the future...
TRANSCRIPT
The 2003 Bam, Iran earthquake: what we knew, what we didn’t know and what we expect in the future
Gareth Funning (University of California, Berkeley) with Eric Fielding (JPL), James Jackson (Cambridge), Barry Parsons & Richard Walker (Oxford), Morteza Talebian (Geological Survey of Iran)
26th December 2003, Mw 6.6
Death toll 26,000
• 26th December 2003, 5.26 am local time
• Mw 6.6
• Official death toll 26,000 (some estimates 40,000+)
• Peak ground acceleration 0.97 g in city centre
• S-P time 1.9 s in city centre (i.e. 14 km from hypocentre)
Tectonic setting
SRTM shaded-relief topography
Bam
Tectonic setting
SRTM shaded-relief topography
Nayband fault
Gowk fault
Sabzevaran faultJebal Barez
mountains
Dasht-e Lut
Bam
Tectonic setting
SRTM shaded-relief topography
Nayband fault
Gowk fault
Sabzevaran faultJebal Barez
mountains
Dasht-e Lut
2003, Mw 6.6
1989, Mw 5.8
1981, Mw 6.6
1998, Mw 6.61981, Mw 7.1
2005, Mw 6.3
Tectonic setting
SRTM shaded-relief topography
Nayband fault
Gowk fault
Sabzevaran fault
Dasht-e Lut
NEIC
Jebal Barez
mountains
Tectonic setting
SRTM shaded-relief topography
Nayband fault
Gowk fault
Sabzevaran fault
Dasht-e Lut
Jebal Barez
mountains
The Bam fault
LANDSAT-7 ETM 541 false colour green=vegetation
Bam
10 km
Baravat
The Bam fault is a prominent ridge running between Bam and Baravat
Walker & Jackson, 2002
The Bam fault
Post-earthquake field surveys found only minor cracking at the foot of the ridge…
Bam
Baravat
Preliminary InSAR data
Bam
10 km
Baravat
First Bam interferogram (each colour cycle=2.8cm of deformation)
Constructed from Envisat ASAR data released for free by ESA
There is a prominent band of incoherence running S of Bam
The Bam earthquake main fault
Interferometric coherenceRed = highBlue = low
Constructed from Envisat ASAR data released for free by ESA
Bam
10 km
Baravat
Low coherence indicates vegetation and surface damage
The Bam earthquake main fault
Surface rupture found in the field – right-lateral offsets of ~20 cm
Bam
10 km
Baravat
The Bam earthquake main fault
Surface rupture found in the field – right-lateral offsets of ~20 cm
Bam
10 km
Baravat
The Bam earthquake main fault
LANDSAT-7 ETM 541 false colour green=vegetation
Bam
10 km
Baravat
There are no surface features corresponding to this fault – we didn’t know it existed
Main fault is ~ 4km west of the mapped Bam fault
Coseismic interferograms
There is an ‘extra’ amount of displacement in the SE quadrant
Ascending interferogram Descending interferogram
Single fault model
Strike 354 dip 84 rake -177 slip 2.2m length 12km top 1.1km b’m 9.3km
Ascending model Descending modelFunning et al., 2005
Single fault model
Large residuals, especially in SE quadrant (rms = 25 mm)
Ascending residual Descending residualFunning et al., 2005
Two fault model (uniform slip)
A ‘teardrop’ feature is reproduced in the SE
Ascending model Descending modelFunning et al., 2005
Two fault model (uniform slip)
Improved fit in SE quadrant (rms = 17 mm)
Ascending residual Descending residualFunning et al., 2005
Two fault model (uniform slip)
LANDSAT-7 ETM 541 false colour green=vegetation
Secondary fault appears to be a southward continuation of the Bam fault
P
SH
Jackson, Bouchon, Fielding, Funning et al., 2006
P
SH
Jackson, Bouchon, Fielding, Funning et al., 2006
two sources
one source
P SH
Jackson, Bouchon, Fielding, Funning et al., 2006
Aftershock distribution
Seismogenic crust may extend ~10 km below the rupture
Jackson, Bouchon, Fielding, Funning et al., 2006
Strong motions & directivity
Rupture velocity of 2.8 km/s ≈ Rayleigh wave velocity
Jackson, Bouchon, Fielding, Funning et al., 2006
Deformation is continuing
Fault zone collapse and postseismic uplift resolved with InSAR
Eric Fielding
Jan 2004-Mar 2006
The Bam earthquake: findings
• The mainshock occurred on a blind fault; not the mapped fault
• Average slip was 2 m at 2–10 km
• The pattern of surface displacements suggests secondary oblique motion on a W-dipping fault
• Seismic data are consistent with 2 sub events
• Significant unruptured fault area may remain