Ground Motion to Intensity Conversion Equations for Iran
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Pure and Applied Geophysics
Ground Motion to Intensity Conversion Equations for Iran SOMAYEH AHMADZADEH,1 GHOLAM JAVAN DOLOEI,1 Abstract—New empirical relations between macroseismic intensity and ground motion parameters including peak ground acceleration and velocity are developed using strong ground motion data and Modified Mercalli Intensity (MMI) information from earthquakes within Iran plateau. The strong motion data consists of 116 three-component waveforms of 23 earthquakes with Mw 5.1–7.3 occurred from 1977 to 2017. The intensity values for each ground motion record were assigned considering the location of accelerograph stations on the isoseismal maps. Simple predictive equations are obtained by fitting a linear model to the mean peak ground motion values applying least squares regression. However, visual inspection of residuals shows magnitude and distance dependency for this set of equations. Improved relationships between ground motion and intensity are derived by comprising magnitude and distance terms as predictive variables. The refined ground motion to intensity conversion equations show smaller variability than simple linear equations in predicting MMI values. Both proposed models are compared with similar relationships in Iran and other regions of the world. The observed discrepancies in relationships may reflect the differences in input data, especially the macroseismic intensity assignments as well as regional variability. The proposed relations can be used for rapid hazard assessments and loss estimation in Iran and surrounding regions. Keywords: Acceleration, motion, intensity, Iran.
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1. Introduction Iran plateau is one of the most seismically active areas in the world with numerous active faults and countless earthquakes (Ambraseys and Melville 1982). Often large earthquakes are accompanying by buildings collapse and losses in rural or urban areas within the plateau. As a result, rapid estimation of strong ground-shaking maps after moderate-to-large earthquakes is of utmost importance to recognize
1 International Institute of Earthquake Engineering and Seismology (IIEES), No. 26, Arghavan St., North Dibajee, 1953714453 Tehran, Iran. E-mail: [email protected]
and HAMID ZAFARANI1
those areas where the largest damage and losses are expected. These maps currently represent an effective and viable tool for emergency management worldwide. In semi-online applications, ground-shaking maps are mainly generated by integrating recorded data and estimates obtained by using ground-motion prediction equations. As the recorded ground-motion parameters became more available, many attempts have been made to correlate seismic intensity with ground motion parameters. Ground motion to intensity conversion equations (GMICE) describe the empirical relationship between recorded ground motions, such as peak ground acceleration (PGA) or peak ground velocity (PGV), and felt intensities. These relations provide possibility of rapid prediction of intensity and probable damages to
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