New Zealand was struck with a 7.8 magnitude earthquake in November 2016. Now, scientists said that the Kaikoura quake, as the event is known, is the most complex recorded. Their findings could also mean higher risks of large earthquakes happening elsewhere and these include the so-called Big One in California.
Individual Faults And Size Of Potential Quakes
Seismologists had long assumed that individual faults and isolated segments of longer faults rupture independent of each other. The idea places a cap on the size of potential earthquakes fault zones can generate
Findings of a new study of the New Zealand earthquake, one of the largest that hit the island in modern history, however, now put this long-held idea into question.
Study researcher Ian Hamling, from the GNS Science in New Zealand and colleagues found that the heavy shaking in the earthquake that occurred just after midnight on Nov. 14, 2016 was due to ruptures of at least 12 different faults. The quake was so strong it was powerful enough to cause seabed to lift out of the water exposing seaweed-covered rocks and marine animals above tide levels.
Some of the faults are so far apart. The faults in one case were separated by more than 15 kilometers (9.3 miles). Separate faults such as these were believed to be immune to the influence of other faults. Hamling said that the long-held idea was that gaps between faults of around 5 kilometers (3.1 miles) stop a rupture from continuing.
Underestimated Seismic Hazards
The findings suggest that scientists may have been misjudging seismic hazards with the idea that slips on isolated faults may not add up to something bigger.
The New Zealand earthquake was far larger that it would have been if it did not jump the gaps. The Kaikoura earthquake ruptured in stages across separate faults, which led to more shaking.
Scientists think that previously unknown connecting faults could be behind this and the faults involved in the earthquake may join up lower in the ground.
Higher Risks Of Magnitude 8 Or Greater Earthquakes Happening
The phenomenon increases the maximum size of a potential earthquake. It also changes the likelihood of bigger earthquakes such as the feared Big One happening. The Big One is the hypothetical earthquake with magnitude 8 or greater expected to happen along California's San Andreas Fault. More faults acting together provide more ways to assemble big earthquakes which increases their likelihood.
"This complex earthquake defies many conventional assumptions about the degree to which earthquake ruptures are controlled by fault segmentation, and should motivate re-thinking of these issues in seismic hazard models," researchers wrote in their study, which was published in the journal Science on March 23.
Given the possibility of several individual faults rupturing simultaneously, the estimated chances of a magnitude 8 or larger earthquake occurring in California in the next three decades increased from 4.7 percent to 7 percent . The chances of smaller earthquakes happening over this period, however, dropped by about 30 percent.
"I think it's a wake-up call," said seismologist Ned Field, from the U.S. Geological Survey in Golden, Colorado.
