A spatial statistical analysis of the occurrence of earthquakes along the Red Sea floor spreading: clusters of seismicit
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ORIGINAL PAPER
A spatial statistical analysis of the occurrence of earthquakes along the Red Sea floor spreading: clusters of seismicity Khalid Al-Ahmadi & Abdullah Al-Amri & Linda See
Received: 28 January 2013 / Accepted: 17 May 2013 # Saudi Society for Geosciences 2013
Abstract The aim of this study is to apply spatial pattern analysis techniques to a seismic data catalog of earthquakes beneath the Red Sea to try and detect clusters and explore global and local spatial patterns in the occurrence of earthquakes over the years from 1900 to 2009 using a geographical information system (GIS). The spatial pattern analysis techniques chosen for this study were quadrant count analysis, average nearest neighbor, global Moran’s I, Getis–Ord general G, Anselin Local Moran’s I, Getis–Ord Gi*, kernel density estimation, and geographical distributions. Each of these techniques was implemented in the GIS so that computations could be carried out quickly and efficiently. Results showed that (1) these techniques were capable of detecting clusters in the spatial patterns of the occurrence of the earthquakes; (2) both global and local spatial statistics indicate that earthquakes were clustered in the study area beneath the Red Sea; (3) earthquakes with higher magnitudes on the Richter scale were notably concentrated in the central and southern parts of the Red Sea where seismic activities were most active; and (4) earthquakes with moderate magnitudes on the Richter scale were particularly concentrated in the northern part of the Red Sea where there is an area of late-stage continental rifting comprised of a broad trough without a recognizable spreading center, although there were several small, isolated deep K. Al-Ahmadi (*) King Abdulaziz City for Science and Technology, Riyadh, Saudi Arabia e-mail: [email protected] A. Al-Amri King Saud University, Riyadh, Saudi Arabia L. See International Institute for Applied Systems Analysis, Laxenburg, Austria L. See Centre for Advanced Spatial Analysis, University College London, London, UK
troughs. We conclude that the pattern analysis techniques applied to the seismic data catalog of earthquakes beneath the Red Sea could detect clusters in the occurrence of earthquakes from 1900 to 2009. Keywords Earthquakes . Clusters . Spatial pattern analysis . Spatial statistics . GIS . Red Sea
Introduction The Red Sea formed during the Eocene–Oligocene period and is one of the world’s youngest oceanic basins (Al-Amri 1995). The boundary between the African and Arabian continental plates follows the principal axis and runs along the entire length of the sea floor (Fig. 1). As the two continental plates are slowly moving apart, the land beneath the Red Sea falls within an active seismic area and experiences frequent earthquakes. The Red Sea is a typical oceanic rift dating back to 5.7 Ma ago (Roeser 1975) and was one of the first areas to be interpreted in the framework of plate tectonics (McKenzie et al. 1970). It is a divergent-type boundary between the African and Arabian plates and is a NN
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