The Southeastern Tehran Earthquake of 17 October 2009 (Mw = 4.0)

Abstract

Tehran and the surrounding area have a history of destructive earthquakes, including several in the last century. Since the presence of diverse faults in this zone confirms its vulnerability to further destructive quakes, it essential to study earthquakes, particularly microearthquakes, to detect active faults in this zone. Existing maps must be corrected and updated, and new and concealed faults determined. An earthquake occurred southeast of Tehran in Tehran Province at 14:23:56.4 local time (GMT 10:53:56.4) on 17 October 2009. The epicenter of the earthquake was determined using seismograms recorded by the International Institute of Earthquake Engineering and Seismology (IIEES) broadband stations at 35.51° N latitude, 51.55° E longitude and 19 km depth. Table 1 shows the estimates of the hypocentral location of the event by the Institute of Geophysics, University of Tehran (IGUT) and the present study. View this table: TABLE 1 Hypocentral Location Investigations conducted about one week prior to the earthquake (Table 2) show the occurrence of 23 microearthquakes with magnitudes lower than Mn = 2.9 in the zone where this event occurred. In the present study, we analyze the 17 October 2009 earthquake and review the seismicity in the last century within the limits of 34.5° and 36.5° N latitude and 50.5° and 52.6 ° E longitude. From spectral studies we obtain the earthquake's source parameters. View this table: TABLE 2 Seismicity of Region One Week before Earthquake (Institute of Geophysics of Tehran University) The Tehran Seismic Telemetry Network at IGUT reports earthquake magnitudes using a local formula and the Nuttli (1973) formula, which is: \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[ M_{n}=\mathrm{log}\left(\frac{{\upsilon}}{2{\pi}}\right)+1.66{ }\mathrm{log}(d)-0.1\] \end{document}(1) where υ is the displacement velocity in nm s–1 and d is the epicentral distance in km. More than 96% of magnitude determinations use the Nuttli formula. The northern areas of Tehran Province form part of the central Alborz mountain range. The areas south of Tehran comprise portions of …