عنوان مقاله [English]
The Iranian plateau, located along the Alpine–Himalayan orogenic belt, is one of the tectonically active regions of shallow crustal earthquakes. Therefore, development of a strong ground-motion dataset with appropriate quality and content is an essential component/tool in local ground-motion studies and for engineering practice.
The first strong-motion instruments were installed in 1973. Since then, the number of strong-motion stations has been gradually increased. Currently, the Iranian strong-motion dataset includes more than 10000 three-component time series, which are recorded at about 1100 permanent stations.
By probing into the quality of the records and the metadata information, 2286 time series recorded on 743 stations from 461 earthquakes with a maximum moment magnitude of 7.3 are chosen. The moment magnitudes have been provided from international or local seismological agencies or from earthquake-specific literature studies in about 40 % of events. For the remaining events, the empirical magnitude conversion equations are used to obtain the more homogenous magnitude information and increase the number of events associated with moment magnitude values. The calculated moment magnitudes are mainly less than 5. The converted moment magnitudes belong to small earthquakes that are originally reported with magnitude scales of Nuttli (MN), Local (ML), body-wave (mb) and surface-wave (Ms).
The bulk of events in the dataset are shallow continental earthquakes with depths less than 30 km. About 75% of events are in this range of the mentioned focal depth. The number of earthquakes with unknown focal depth is less than 1% in the selected dataset. The events of depths ranging more than 40 km are mainly from the Zagros region. For about 66% of events, there is no information available (NA) about their faulting mechanisms. The dominant faulting mechanisms are reverse (20% of events) and strike-slip faulting (12% of events). A minority of events and accelerograms are related to the normal faulting mechanism.
Most of the unknown faulting mechanisms are attributed to events with small magnitude (Mw ≤ 5) due to the lack of double-couple fault-plane solutions for these earthquakes. Large events have been studied to determine the faulting mechanisms due to their importance while on the small events are rarely focused.
About 743 stations have provided accelerometric data in the selected dataset. The average shear-wave velocity between 0 m and 30 m depth (Vs30) in more than 40% of these stations have been measured and reported by the BHRC. The site classes for about 299 stations have been proposed either by geological surveys or by empirical methods (using H/V method). Therefore, we have no information about the soil categories for only 138 stations because they are either temporary stations or stations that recorded accelerograms less than 5 times. Considering the Vs30 criteria, the majority of the stations are belonged to site class II while the most of the stations will be in site class III if we use only the above-mentioned empirical method.
During the data processing, the records with the following features have been eliminated from the dataset: data from instruments that triggered during the S-wave train; the records with only a single horizontal component; and the records obtained from events with unknown or poor estimates of magnitude (which are attributed to the small
events). Furthermore, the records with non-standard error such as very high-frequency spikes, multi-event, and so on are excluded from the dataset.
The aim of this paper is first to present the new catalog with comprehensive metadata for engineering and research practices. The record selection for development of new GMPEs for various strong-motion parameters can be performed by using the provided catalog. In addition, the main features of the Iranian strong-motion dataset have been provided in this paper. To this end, a careful revision of the characteristics of the earthquakes such as location, magnitude, style of faulting and fault rupture plane geometry, if available, has been scientifically performed for the first time using the best available information. Finally, we concentrate on special ground-motion records including records with peak ground acceleration PGA > 300 cm/s/s and distances less than 30 km. These are designated as “distinct” records in the Iranian dataset because they include less than 2% of the selected dataset.