The 1998 March 14 Fandoqa earthquake (M_w6.6) in Kerman province, southeast Iran: re-rupture of the 1981 Sirch earthquake fault, triggering of slip on adjacent thrusts and the active tectonics of the Gowk fault zone

Abstract

SUMMARY The 1998 March 14 Fandoqa earthquake (Ms 6.6) was the penultimate in a series of five substantial earthquakes on the Gowk fault system of southeast Iran since 1981, all of which were associated with co‐seismic surface ruptures. We use observations of surface faulting, analysis of P and SH body waves, SAR interferometry and geomorphology to investigate the ruptures in these earthquakes and how they are related both to each other and to the regional active tectonics. The 1998 Fandoqa earthquake produced 23 km of surface faulting with up to 3 m right‐lateral strike‐slip and 1 m vertical offsets. SAR interferometry and seismic waveforms show that the main rupture plane dipped west at ∼50° and had a normal component, although the surface ruptures were more complicated, being downthrown to both the east and the west on steep faults in near‐surface sediments. In addition, SAR interferometry shows that a nearby thrust with a similar strike but dipping at ∼6°W moved about 8 cm in a time interval and in a position that makes it likely that its slip was triggered by the Fandoqa earthquake. The 1998 surface ruptures in the Gowk valley followed part of a much longer (∼80 km) set of co‐seismic ruptures with smaller offsets that were observed after larger earthquakes in 1981 (Mw 6.6 and 7.1). The main ruptures in these 1981 earthquakes probably occurred on different, deeper parts of the same fault system, producing only minor reactivation of the shallower faults at the surface. Although the 1981–1998 earthquake sequence apparently ruptured parts of the same fault system repeatedly, these earthquakes had very different rupture characteristics: an important lesson for the interpretation of both palaeoseismological trenching investigations and historical accounts of earthquakes. The regional kinematics, which involve oblique right‐lateral and convergent motion, are evidently achieved by a complex configuration of faults with normal, reverse and strike‐slip components. Some of the complexity at the surface may be related to a ramp‐and‐flat fault geometry at depth, but could also be related to the large topographic contrast of ∼2000 m across the fault system, which separates the high Kerman plateau from the low Dasht‐e‐Lut desert. Details of the fault geometry at depth remain speculative, but it must be unstable and evolve with time. It may be this requirement that causes the principal features of geological ‘flower structures’ to develop, such as series of subparallel faults which accommodate dip‐slip components of motion.

Fault mechanics and post-seismic deformation at Bam, SE Iran

“…The sharp step in elevation across the escarpment requires that dip-slip fault motion extends to near the surface. Similar structures have been recognized elsewhere in Iran such as at Tabas-e-Golshan (Walker et al 2003), Ferdows (Walker et al 2003), Sefidabeh (Berberian et al 2000), Rigan (Walker et al 2013) and Shahdad (Berberian et al 2001).…”

“…Earthquakes that ruptured the top and bottom half of the seismogenic layer in separate events have been documented elsewhere (Berberian et al 2001;Elliott et al 2011) and can be explained by loading of the unruptured part of the fault following the earlier earthquake. Of these examples, the Qaidam earthquakes were separated by 10 months (Elliott et al 2011), and the Golbaf-Sirch earthquakes by 17 yr (Berberian et al 2001), showing that failure of the loaded half of the seismogenic layer can occur on timescales much shorter than the recurrence interval for faults in central and eastern Iran, which is generally >1000 yr (Fattahi et al 2006;Walker et al 2010). …”

GPS Strain Rate and Seismic Activity Before the Ludian Earthquake (Ms 6.5), Northeast Yunnan, China: New Implications for Eastward Chuan-Dian Block Extrusion

“…However, the resolution of this issue is constrained by the sparse density of GPS measurements, especially the low number of vertical velocity values. Another uncertainty is that the sliprate change is complicated by the asperity distribution of the fault zone at depth, the faulting segmentation on the surface and the far-field effect from plate collision (e.g., East Iran; Berberian et al 2001;Walker et al 2010). Even so, this issue is important as it impacts the utility of time-averaged slip-rate estimates in constraining the present-day seismic hazard posed by individual faults.…”

Probabilistic seismic hazard maps for the sultanate of Oman

“…The catalogue is built by merging historical and instrumental data. In addition, the following studies on specific events or region were also consulted to gather additional information regarding earthquakes of considerable size (Berberian 1973;Quittmeyer 1979;Jackson and Fitch 1981;Alsinawi 1983;Jackson and McKenzie 1984;Baker et al 1993;Berberian 1995;Berberian and Yeates 1999;Berberian et al 2001;Maggi et al 2002;Talebian and Jackson 2004;Walker et al 2005;Rodgers et al 2006;Al Marzooqi et al 2008). …”