M 7.3 - 50 km SW of Dongning, China

Tectonic Summary

The June 28, 2002, M 7.3 earthquake near the Jilin-Heilongjiang border region of China occurred as the result of deep reverse faulting within the subducted Pacific plate, approximately 565 km beneath northeastern China and 1,300 km west of the Japan Trench, where the oceanic Pacific plate begins its descent into the mantle. Focal mechanism solutions indicate that rupture occurred on either a steeply dipping reverse fault or a very shallowly dipping thrust fault. Slip on a fault of either orientation would accommodate the down-dip compression of the Pacific slab that is implied by the normal-component of the faulting solution. At the location of the earthquake, the Pacific plate subducts at a rate of about 90 mm/yr.

The locations of intermediate-depth and deep earthquakes form features known as Wadati-Benioff zones that image their associated tectonic plate’s descent into the mantle. The June 28th earthquake occurred near the base of its particularly long and straight Wadati-Benioff zone that is well-imaged in the accompanying cross-section (see earthquake summary poster). Since 1972, this segment of the subducted Pacific plate has produced 11 earthquakes with focal depths between 400 and 600 km and with magnitudes of 6+.

Earthquakes that have focal depths greater than 300 km are commonly termed “deep-focus” earthquakes. Deep-focus earthquakes cause less damage on the ground surface above their foci than similar-magnitude shallow-focus earthquakes, but large deep-focus earthquakes may be felt at great distance from their epicenters. The largest recorded deep-focus earthquake prior to this June 2002 earthquake was a M 8.2 event that occurred at a depth of 630 km within the subducted Nazca plate beneath South America near the northern Bolivian border in 1994. A larger event has since occurred—namely the M 8.3 earthquake that occurred at a depth of 600 km within the subducted Pacific plate beneath the Sea of Okhotsk offshore of northeastern Russia in 2013. The M 8.3 Sea of Okhotsk earthquake was felt all over Asia, as far away as Moscow, and across the Pacific Ocean along the western seaboard of the United States (though at distant locations, individuals reporting having felt the event were likely very favorably situated for the perception of small ground motions). The M 8.2 Bolivian deep-focus earthquake in 1994 had similarly been reported by individuals in North America at great distance from the epicenter.

Over the past century, 68 earthquakes with a magnitude of M 7+ have occurred at depths greater than 300 km globally; two of these were located in the same region as the June 28, 2002 event. The closest was a M 7.1 earthquake in April 1999, roughly 30 km to the southwest and at the same depth.

Hayes et al. (2016) Tectonic summaries of magnitude 7 and greater earthquakes from 2000 to 2015, USGS Open-File Report 2016-1192. (5.2 MB PDF)