Systematic relocation of early instrumental seismicity: earthquakes in the International Seismological Summary for 1960-1963

We relocate the 2,556 events reported in the bulletins of the International Seismological Summary (ISS) during the period 1960-1963, both inclusive. Phase arrival time data were obtained partially in digital form from the International Seismological Centre (ISC) and the rest by scanning the printed bulletins and applying optical character recognition. Earthquakes have been relocated using a teleseismic location method that uses recent and accurate travel time tables, depth phases, and incorporates corrections for ellipticity, bounce-point bathymetry/topography, and near-station velocity structure. Blatant mislocations (such as earthquakes deeper than 100 km below mid-ocean ridges) have been corrected, and the newly obtained locations are similar in quality to those in the early ISC bulletins. Two significant earthquakes occurred during the studied time period: the Mw=9.6 Great Chilean earthquake (May 22nd, 1960) and the Mw=8.6 Kurile earthquake (October 13th, 1963), and we present a detailed analysis of the main shock locations and aftershock distributions. This work, and its continuation back in time before 1960, will increase the time period for which reliable and homogeneously determined hypocenters are available for global seismicity studies.