The first tremor occurred at 18:35 UTC (04:35 local time) and was of magnitude 7.2, but though there are about 16000 people living within 100 km little disruption was caused as the hypocentre was measured to be at a depth of roughly 380km.
The second earthquake was six times less powerful (M6.6) and had an epicentre located 500km from the first, putting it in the vicinity of 140,000 inhabitants. This earthquake was much more of a threat as it was only ~60km deep, though no damage has been reported.
Below: USGS shaking intensity map for the second earthquake. Colour key at the bottom.
Had the earthquake originated from the interaction between the two plates the hypocentre would have been much shallower and a tsunami would likely have resulted. USGS issued a precautionary warning but said it was unlikely to occur.
Below: Location of the first M7.2 earthquake (red lines show margin types). Australian plate to south east; Pacific plate to north and west
USGS (first earthquake hypocentre 378km deep)
EMSC (first earthquake hypocentre 383km deep)
Thomas Ruddell, 25/07/2013