3. EARTHQUAKE EFFECTS
The following descriptions of surface manifestations are represented in Fig. 6.
Study of the Landsat imageries (A and B) at a scale of 1:1,000,000 and 1:500,000, aerial photographs of the region at a scale of 1:20,000 and 1:55,000, the existing geological maps(B.P. 1963 IOOC 1969) and detailed field study shows that there are only four major faults in or near the Naghan epicentral region, namely the Ardal Fault, Shalamzar Fault, Dopolan Fault and Dena Fault
fig. 5. Seismotectonic subdivision of the Zagros Active Folded belt.1. Ahvaz Seismotectnic Province, 2. Hormoz Seismotectonic provine,3. instrumental epicenter 1900-1976,4. towns destroyed by destructive earthquakes(A.D.),5. high angle reverse fault,6. thrust Zone (high Zagros),10. northern limit of stable area (after Berberian,1976b).
Ardal Fault: This is a NW-SE reverse fault 80 km long, on the southeastern end of which the epicentral region is situated (Figs. 6 and 7). It deepens towards the northeast. A linear Hormoz salt plug is intruded along its northwestern part. The fault is covered by Quaternary alluvial deposits.
Shalamzar Fault: This fault is situated north of the epicentral region. Its length is about 60 km and it deepens towards the northeast (Fig. 6).
Dopolan Fault: This is another northwest-southest fault 65 km long, southwest of the epicentralregion.lt starts from Dopolan in the NW and joins the Dena fault at its southeastern extremity (Figs. 6 and 8)
Dena Fault: a NNW-SSE fault about 30 km southeast of the epicentral region. It seems that the macroseismic epicentre of Sarpir earthquake of 21.9.1975 was located on this fault (southeastern corner of Figure 6).
During a very careful investigation, these faults were checked in their entirety, and they were not reactivated at surface during the Naghan earthquake. Neither was the earthquake associated with the formation of new surface faults.
3.2. Salt Domes
There are two late Precambrian salt domes (Hormoz salt) in the Naghan region
intruded along Ardal and Dena faults: the Ardal salt dome in the northwestern part
of the epicentral region, and the Dena salt dome in the southeastern part of the region
During the field investigation the contacts of the salt domes with the adjacent rocks have been carefully checked, but no fresh movement was found.
3.3. Landslides and Displacement of Stones
Several large scale landslides occurred during the Naghan earthquake, including one about 1 km in length north and northwest of Ardal near the Ardal fault. The strike of this linear landslide is about N150°E (Fig. 9).
Another landslide destroyed a vineyard and moved towards Sakiabad village, pushing, fissuring and destroying a few houses in the village (Figs. 10 and 11). Some landslides on the way to Ardal destroyed parts of the road (Figs. 12 and 13).
Many stones in Quaternary alluvial deposits were upthrown and displaced during the earthquake (Fig. 14).
(Facing page)Fig. 6. Map of the Naghan(Iran) earthquake area showing the main tectonic and damage features. The intensity grades correspond to the Modified Mercalli Scale (I0 = VIII). 1. Severely damaged, 2. Considerable damage, 3. Light damage, 4. The shock strongly felt, 5. Instrumental epicentre, 6. Fault, 7. Isoseismals of Naghan 6.4. 1977 earthquake, 8. Isoseismals of Sarpir 21.9.1975 earthquake, 9. Distance between macroseismic and microseismic epicentres.
Fig. 7. Ardal Fault, NW of Ardal village at Ab-Beheshtabad river. Note that this high angle reverse fault is covered by the Quaternary alluvial seposits. Looking west. No evidence of reactivation of this fault ahs been obwerved at surface during the Naghan earthquake of 6April 1977. The Sarvak Formation along the Ardal high angle reverse fault is upth-rusted and faces the southern quaternary alluvial deposits. Looking NW
Fig. 8. Dopolan fault at Tang-e-Laghar, south of the epicentral region. No evidence of reactiva-tion of this fault been observed at surface during the Naghan earthquake of 6 April1977. The Sarvak Formation(Middle Cretaceous limestones)in the north faces the pabdeh Formation(Eocene)in the south. Looking NW.
Fig. 9. A long crack of N150°E direction northwest of Arsal formed due fo a large landslide. Looking E.
fig. 10. Landslide near Sakiabad which cut the vineyard moved towards the village, damaging houses. Looking SW.