In the week or two before the magnitude-8.6 Indian Ocean earthquake in 2012, Earth was unusually quiet, with few large quakes over magnitude 5. Afterward, seismic activity all over the globe was elevated for more than a week. Then, suddenly, global seismicity dropped off precipitously: Beginning two weeks after the mainshock, no earthquakes of magnitude-6.5 or greater occurred for 95 days.
In 1964, a magnitude-9.2 earthquake ruptured two segments of the Alaskan megathrust fault along more than 900 kilometers from Prince William Sound to Kodiak Island. Historical and paleoseismic evidence has hinted at previous events in this region in 1788 and about 1100, and now a team working on Kodiak Island has found clues of another large event that struck about 500 years ago. The find makes the recurrence interval for the tsunami-producing fault much shorter, potentially increasing the earthquake and tsunami hazard profile, not only for Alaska, but also Hawaii and California.
Californians are bracing for when the San Andreas Fault unleashes the next “big one,” but a new study looking at the paleoseismic history of the San Francisco Bay Area suggests that accumulated stress could also be released in a series of moderate to large quakes on satellite faults, rather than by a single great event on the San Andreas.
For decades, Istanbul has been bracing for a major earthquake from the dangerously active North Anatolian Fault, which passes just 20 kilometers south of Turkey’s largest city. A new study looking at the age of the fault zone may set a cap on the maximum quake size that could hit Istanbul, suggesting that the older, more mature sections of the zone in the east are capable of bigger earthquakes than the younger sections in the west, which are near the city.
Occurrences of earthquakes in the Central and Eastern United States have increased since 2009 — a phenomenon that many scientists attribute to the growing use of hydraulic fracturing for fossil fuel extraction. Most agree that it’s not the fracturing itself, but the reinjection of wastewater into wells for containment beneath the surface that tends to induce seismic activity. Now, new research looking at the effects of induced seismic activity suggests that human-made earthquakes and naturally occurring tectonic earthquakes are felt differently at the surface.
More than 13 million people live in Tokyo, a city that has been devastated by earthquakes in the past and is likely to be rocked again. Since the massive magnitude-9 Tohoku earthquake and tsunami in March 2011, recurrence intervals for nondamaging slow-slip quakes beneath Japan’s capital have shortened. And that has left seismologists to wonder if this aseismic creep could be signaling a countdown to Tokyo’s next “big one.”
One of the most famous pictures of the San Andreas Fault — taken by G.K. Gilbert, the pioneering geologist whose late-19th century insights into faults and the earthquake cycle were close to prescient — shows a woman standing next to the ruptured fault immediately after the 1906 earthquake.
Many of the world’s richest gold deposits are found in fault zones, where the precious metal is concentrated in quartz veins that cut through the surrounding rock. For several decades, scientists have suspected that earthquakes help form these deposits by releasing pressure and giving metals in mineral-rich hydrothermal fluids in the fault zone a chance to precipitate. But clear evidence for this so-called “fault-valve” process has been hard to come by. Now, researchers studying the geochemical makeup of tiny pyrite crystals from one well-known gold mine appear to have found some long-sought confirmation.
In this era of high-tech seismic networks and GPS, scientists still rely on low-tech earthquake intensity scales, generated from public surveys like the U.S. Geological Survey’s (USGS) Did You Feel It? questionnaire, to characterize ground shaking in places with low instrument coverage. But how accurate are people’s perceptions of shaking?
During the April 18, 1906, magnitude-7.9 earthquake near San Francisco, Calif., 470 kilometers of the San Andreas Fault ruptured between San Juan Bautista, south of San Francisco, and Point Arena, north of the city.