The 2003 Bam, Iran earthquake: what we knew, what we didn’t know and what we expect in the future

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

Tectonic setting

• SRTM shaded-relief topography

Tectonic setting

• SRTM shaded-relief topography

Tectonic setting

• SRTM shaded-relief topography

Tectonic setting

• SRTM shaded-relief topography

Tectonic setting

• SRTM shaded-relief topography

The Bam fault

• LANDSAT-7 ETM 541 false colour green=vegetation

The Bam fault

• Post-earthquake field surveys found only minor cracking at the foot of the ridge…

Preliminary InSAR data

• First Bam interferogram (each colour cycle=2.8cm of deformation)

• Constructed from Envisat ASAR data released for free by ESA

The Bam earthquake main fault

• Interferometric coherence

• Red = high

• Blue = low

• Constructed from Envisat ASAR data released for free by ESA

The Bam earthquake main fault

• Surface rupture found in the field – right-lateral offsets of ~20 cm

The Bam earthquake main fault

• Surface rupture found in the field – right-lateral offsets of ~20 cm

The Bam earthquake main fault

• LANDSAT-7 ETM 541 false colour green=vegetation

Coseismic interferograms

• There is an ‘extra’ amount of displacement in the SE quadrant

Single fault model

• Strike 354 dip 84 rake -177 slip 2.2m length 12km top 1.1km b’m 9.3km

Single fault model

• Large residuals, especially in SE quadrant (rms = 25 mm)

Two fault model (uniform slip)

• A ‘teardrop’ feature is reproduced in the SE

Two fault model (uniform slip)

• Improved fit in SE quadrant (rms = 17 mm)

Two fault model (uniform slip)

• LANDSAT-7 ETM 541 false colour green=vegetation

Aftershock distribution

• Seismogenic crust may extend ~10 km below the rupture

Strong motions & directivity

• Rupture velocity of 2.8 km/s ≈ Rayleigh wave velocity

Deformation is continuing

• Fault zone collapse and postseismic uplift resolved with InSAR

The Bam earthquake: findings