Sefidabeh Earthquake of 23 February 1994, mb 6.6
In February 1994 a sequence of four earthquakes with magnitudes (Ms) 5.5- 6.1 occurred in the space of a week in a remote area of eastern Iran. The first event occurred on 23th February 1994 with magnitude of mb=6.6. The dominant characteristic of the surface ruptures is bedding-plane slip, producing extensional features on the ridge. From the seismological and geomorphologic evidences, it appears that these ruptures formed in response to the growth of an anticline above a blind thrust. Berberian et al. (2000) observed that the ruptures were all within the vertically dipping and isoclinally folded Upper Cretaceous Paleocene flysch and volcaniclastic rocks, and nearly all involved slip on bedding planes. The ruptures and scarps formed three types of surface feature: 1) Discontinuous mini-grabens formed by doubl scarps and up to 1.7m deep occurred along the Sefidabeh ridge crest, with slip occurring on sub vertical bedding planes mostly in flysch. These grabens are well developed 1.2km south of the gap in the ridge occupied by the old lake deposits adjacent to Sefidabeh. Striations on the bedding planes showed subvertical dip slip, with no strike-slip component. The larger displacement was usually on the western wall of the minigrabens. Exposures in gullies show that the 1994 movement increased previous offsets of at least 5.0 m on the same bedding planes, and that the saddle-like morphology of the ridge crest is the result of previous graben-forming movements. 2) Step-like single scarps were also common on the Sefidabeh ridge, usually on the NE side and upthrown to the SW, again on subvertical bedding planes. 3) Other scarps on the ridge appeared to have formed by settlement of soft tuff. Beds between competent limestone layers, perhaps in response to the collapse of underground channels or caverns. Berberian et al. (2000) noted that in any case, the early Tertiary deformation that caused tight isoclinals folding in the soft shale and flysch formations produced more discontinuous faulting within the harder limestones and tuffs, and there is no certainty that the vertical bedding-plane shear seen at the surface extends to any great depth (Jafari and Moosavi, 2008).
The most important worldwide earthquakes on this day
| Date | Time | Y | X | Depth | Mw | Region | Refrence |
| 958/2/23 | – | 36.00 | 51.10 | – | 7.7 | Rey | Amb |
| 1949/2/23 | 16:08:11 | 41.865 | 84.191 | 10 | 7.3 | southern Xinjiang, China | USGS |
| 1969/2/23 | 0:36:58 | -3.201 | 118.904 | 15 | 7 | Sulawesi, Indonesia | USGS |
| 1970/2/23 | – | 27.771 | 54.54 | 25 | 5.8 | southern Iran | USGS |
| 1980/2/23 | 5:51:03 | 43.53 | 146.753 | 44 | 7 | Kuril Islands | USGS |
| 1994/2/23 | 8:2:4 | 30.853 | 60.596 | 6 | 6.1 | Sefidabeh- E Iran | NEIC |