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, M w 6.6 Death toll 26,000 26th December 2003, 5.26 am local time M w 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 fault Jebal Barez mountains Dasht-e Lut Bam

Tectonic setting SRTM shaded- relief topography Nayband fault Gowk fault Sabzevaran fault Jebal Barez mountains Dasht-e Lut 2003, M w , M w , M w , M w , M w , M w 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 coherence Red = high Blue = 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 model Funning et al., 2005

Single fault model Large residuals, especially in SE quadrant (rms = 25 mm) Ascending residual Descending residual Funning et al., 2005

Two fault model (uniform slip) A ‘teardrop’ feature is reproduced in the SE Ascending model Descending model Funning et al., 2005

Two fault model (uniform slip) Improved fit in SE quadrant (rms = 17 mm) Ascending residual Descending residual Funning 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 PSH 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