تعيين پارامترهاي هشدار سريع زلزله τC و Pd براي جنوب ايران (تنگه هرمز)

Determination of earthquake early warning parameters, xc and Pd, in southern Iran

During the past decades, attempts have been made to develop an early warning system for coming destructive earthquakes a few seconds before the ongoing ground motion. In this paper, a practical method for the early warning of earthquakes in south Iran is presented. This region is selected for study because it has high potential for generating earthquakes and has a more complete strong ground motion data set. Earthquake early warning systems have the potential to reduce the damaging effects of earthquakes by giving a few seconds to a few tens of seconds warning before the arrival of damaging ground motion. Using P-wave arrivals is the most rapid method of delivering earthquake early warning and may permit a few seconds warning of ongoing ground motion in the region. To rapidly assess the damaging potential of an earthquake for purposes of earthquake early warning in southern Iran, we determined a ground-motion period parameter xc and a high-pass filtered displacement amplitude parameter Pd from the initial 3 s of the P waveforms. The tc is called source parameter and is related to the magnitude of earthquakes. Our study indicates that ic is independent of epicentral distance up to 130 km. In practice, we calculate tc for distances less than 100 km. We use the peak displacement and acceleration amplitudes of the first 3 sec of the vertical-component records. At a given site, we estimate the magnitude of an event from tc and the peak ground-motion velocity (PGV) from Pd. The region of study contained 42 strong ground motion accelometers that have been deployed in the region since 1977. About 419 strong motion digital data from 209 local earthquakes that were recorded during 1977-2006 in the study region, are extracted for this study. Among these earthquakes, 194 with magnitudes greater than 3 were used for this analysis. For determination of Pd, we used 152 waveform data with epicentral distance less than 44 km. The P-wave onset time readings were carried out by SAC software out the vertical components. We found that the peak initial-displacement amplitude Pd correlates well with the peak ground-motion velocity (PGV) at the same site. We selected the earthquake with M > 3 that was recorded during 1975-2006 by near field strong ground motion instruments in the region, operated by the Building and Housing Research Center. The vertical components of accelerations were converted to ground velocity and displacement. The displacements are filtered with a one-way Butterworth high-pass filter with a cut-off frequency of 0.075 Hz. From the vertical components, tc and Pd are computed. We found the relationship between xc and magnitude (M) and between Pd and PGV for this region. These two relationships can be used to detect the occurrence of a major earthquake and provide onsite warning around the station. The quality of data was increased by increasing the signal to noise ratio. Also, more recording stations produce less scatterings and errors. The results indicate that earthquakes with magnitudes greater than magnitude 5, have greater tc . Thus, by using the obtained relationships in this study, from the first 3 seconds of initial P-waves, we can estimate the magnitude of earthquakes. Also, we can clarify whether the occurring earthquake could be destructive and early warning issue might be necessary. The high seismic activity of Bandar-Abbas, the port city at the Strait of in Hormoz, in southern Iran, highlights the necessity and importance of a dense seismic network and an early warning system to be deployed in the region in order to detect the location and the magnitude of damaging earthquakes for the purposes of reducing the damaging affects of earthquakes by giving a few to a few tens of seconds warning before the arrival of damaging ground motion.