The latest New Zealand earthquake was a deadly combination of distance, depth and timing.
While weaker than the one that rocked the area last September, it did more damage and cost lives, primarily because of its location.
Tuesday's magnitude-6.3 quake was centered about 3 miles from the populated hub of Christchurch, toppling buildings, killing dozens and trapping others. It was also only about 3 miles deep and occurred during the middle of a workday when commercial buildings were filled with employees.
The jolt "is squarely beneath the city itself," said seismologist Egill Hauksson of the California Institute of Technology. "All the old historic buildings are being shaken more violently than they were built to withstand."
Scientists classified it as an aftershock of the powerful magnitude-7 that struck last Sept. 4.
