Chris Goldfinger, associate professor of marine geology and geophysics at Oregon State University, and colleagues published their results in the April issue of BSSA as part of a special section on the 1906 San Francisco earthquake. BSSA is published by the Seismological Society of America (SSA), which was created in response to the 1906 earthquake.
Using marine sediment cores collected along the northern California seabed, researchers identified 15 turbidites, which are sediment deposits generated by submarine landslides and commonly triggered by earthquakes. The 15 turbidites, including one associated with the great 1906 earthquake, and the corresponding land paleoseismic record establish an average recurrence rate of approximately 200 – 240 years for the San Andreas Fault.
In a parallel study, they found that during the same period, 13 of these 15 San Andreas earthquakes occurred at almost the same time as earthquakes along the southern Cascadia Subduction Zone, which stretches from northern Vancouver Island to northern California. The marine and land paleoseismic record suggest a recurrence rate of approximately 220 years for the southern Cascadia fault, which is substantially shorter than the 600-year cycle suggested by previous research for full ruptures in Cascadia.
The Cascadia earthquakes also preceded the San Andreas earthquakes by an average of 25 to 45 years. “It’s either an amazing coincidence or one fault triggered the other,” said Goldfinger. The generally larger size of the Cascadia earthquakes, and the timing evidence suggests Cascadia may trigger the San Andreas Two seismic events on the San Andreas were apparently not associated with Cascadia, including the 1906 earthquake which followed the previous Cascadia earthquake by approximately 200 years.
Goldfinger and his colleagues collected core samples that cover the past 10,000 years, and the next step involves analyzing this data for further evidence of a corollary relationship between the plate boundary faults for earlier periods of time. “This type of relationship doesn’t just happen accidentally. We expect the temporal relationship, if correct, to show itself over the longer period of time,” said Goldfinger.
Perhaps the most thoroughly studied seismic event, the 1906 quake continues to fascinate seismologists. BSSA’s special section considers the landmark event, which was initiated along the San Andreas Fault just off the San Francisco coast on April 18, 1906. The strong shaking caused widespread damage along the 300 miles of the fault in northern California, reducing much of San Francisco to rubble.
“The directivity of the ruptures, north to south, which is implied by this study, will have significant meaning for seismic hazard models for San Francisco,” said Goldfinger. The 1906 earthquake, which is an exception to the pattern over the past 3000 years, ruptured in both directions, but mostly from south to north.
“Lessons from the 1906 earthquake should apply to similar faults and earthquakes elsewhere,” writes Brad T. Aagaard, a research geophysicist at the USGS Menlo Park and co-author of the introduction to the special section and two papers that focus on ground motion. “As our understanding of earthquakes evolves and the technology to increase our knowledge develops, there is much to be gained by revisiting older events.
In 1906, approximately 600,000 people lived in the greater Bay Area, about 10 percent of today’s population. Today’s cities have high rise buildings, people travel by car, and five major bridges connect the major cities around the San Francisco Bay.
The special section features new research that characterizes the earthquake source, refines assessments of ground shaking that support higher intensities, and explores the possible effects of a repeat of the 1906 earthquake, or similar-sized earthquakes on the San Andreas Fault.
Research by Aagaard et al., demonstrates how the variability in strong shaking over the San Francisco Bay area observed in 1906 can be attributed to the geologic structure and rupture characteristics. More importantly, by considering other possible rupture scenarios, the Aagaard et al., conclude that future large earthquakes along the San Andreas Fault may subject the San Francisco Bay Area to stronger shaking than occurred in the 1906 earthquake.
Nan Broadbent | EurekAlert!
Greenland ice flow likely to speed up: New data assert glaciers move over sediment, which gets more slippery as it gets wetter
17.08.2017 | Swansea University
Climate change: In their old age, trees still accumulate large quantities of carbon
17.08.2017 | Universität Hamburg
Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.
As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...
Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.
Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...
For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.
While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...
An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.
The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...
A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.
Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...
16.08.2017 | Event News
04.08.2017 | Event News
26.07.2017 | Event News
21.08.2017 | Materials Sciences
21.08.2017 | Health and Medicine
21.08.2017 | Materials Sciences