Megathrust quake faults weaker and less stressed than thought
2015-09-10
(Press-News.org) MENLO PARK, Calif. -- Some of the inner workings of Earth's subduction zones and their "megathrust" faults are revealed in a paper published today in the journal Science. U.S. Geological Survey scientist Jeanne Hardebeck calculated the frictional strength of subduction zone faults worldwide, and the stresses they are under. Stresses in subduction zones are found to be low, although the smaller amount of stress can still lead to a great earthquake.
Subduction zone megathrust faults produce most of the world's largest earthquakes. The stresses are the forces acting on the subduction zone fault system, and are the forces that drive the earthquakes. Understanding these forces will allow scientists to better model the physical processes of subduction zones, and the results of these physical models may give us more insight into earthquake hazards.
"Even a 'weak' fault, meaning a fault with low frictional strength, can accumulate enough stress to produce a large earthquake. It may even be easier for a weak fault to produce a large earthquake, because once an earthquake starts, there aren't as many strongly stuck patches of the fault that could stop the rupture," explained lead author and USGS geophysicist Hardebeck.
Although the physical properties of these faults are difficult to observe and measure directly, their frictional strength can be estimated indirectly by calculating the directions and relative magnitudes of the stresses that act on them. The frictional strength of a fault determines how much stress it can take before it slips, creating an earthquake.
Evaluating the orientations of thousands of smaller earthquakes surrounding the megathrust fault, Hardebeck calculated the orientation of stress, and from that inferred that all of the faults comprising the subduction zone system have similar strength. Together with prior evidence showing that some subduction zone faults are "weak", this implies that all of the faults are "weak", and that subduction zones are "low-stress" environments.
A "strong" fault has the frictional strength equivalent to an artificial fault cut in a rock sample in the laboratory. However, the stress released in earthquakes is only about one tenth of the stress that a "strong" fault should be able to withstand. A "weak" fault, in contrast, has only the strength to hold about one earthquake's worth of stress. A large earthquake on a "weak" fault releases most of the stress, and before the next large earthquake the stress is reloaded due to motion of the Earth's tectonic plates.
INFORMATION:
ELSE PRESS RELEASES FROM THIS DATE:
2015-09-10
Researchers from the MRC Centre for Developmental Neurobiology (MRC CDN) at the Institute of Psychiatry, Psychology & Neuroscience (IoPPN), King's College London, have discovered a new molecular 'switch' that controls the properties of neurons in response to changes in the activity of their neural network. The findings, published in Science, suggest that the 'hardware' in our brain is tuneable and could have implications that go far beyond basic neuroscience - from informing education policy to developing new therapies for neurological disorders such as epilepsy.
Computers ...
2015-09-10
WASHINGTON, D.C. - Since 2002, the Southern Ocean has been removing more of the greenhouse gas carbon dioxide from the atmosphere, according to two new studies.
These studies make use of millions of ship-based observations and a variety of data analysis techniques to conclude that that the Southern Ocean has increasingly taken up more carbon dioxide during the last 13 years. That follows a decade from the early 1990s to 2000s, where evidence suggested the Southern Ocean carbon dioxide sink was weakening. The new studies appear today in the American Geophysical Union ...
2015-09-10
A prospective longitudinal study of U.S. Marines suggests that reduced heart rate variability - the changing time interval between heartbeats - may be a contributing risk factor for post-traumatic stress disorder (PTSD). The findings are reported in the September 9 online issue of JAMA Psychiatry by researchers at the University of California, San Diego School of Medicine and Veterans Affairs San Diego Healthcare System.
Even at rest, the normal rhythm of the heart fluctuates, reflecting influences and changes in other parts of the body. Generally speaking, the greater ...
2015-09-10
Imagine the scientific discoveries that would result from a searchable online database containing millions of plant, algae, and fungi specimen records. Thanks to a new set of workflow modules to digitize specimen collections currently preserved in herbaria, something like that might be within reach. The modules are provided by the National Science Foundation's (NSF) Integrated Digitized Biocollections (iDigBio), which is facilitating a collective effort to unify digitization projects across the nation.
"North America's herbaria curate approximately 74 million specimens ...
2015-09-10
COLUMBUS, Ohio - Would a color by any other name be thought of in the same way, regardless of the language used to describe it?
According to new research, the answer is yes.
A new study examines how a culture of nomadic hunter-gatherers names colors, and shows that they group colors into categories that align with patterns of color grouping evident in 110 other world languages.
This study population - the Hadza people of Tanzania - has relatively few commonly shared color words in its language. During the study, the most common response by Hadza participants to a ...
2015-09-10
Seasonal flare-ups in patients with multiple sclerosis are caused by plummeting levels of melatonin in the spring and summer, according to research published September 10 in Cell. The study reveals that relapses in patients with this autoimmune disorder are much less frequent in the fall and winter, when levels of the so-called darkness hormone are at their highest, but the reverse is true in the spring and summer seasons.
Moreover, treatment with melatonin improved clinical symptoms in a mouse model of multiple sclerosis by restoring a healthy balance of immune cells ...
2015-09-10
The blame for some of chemotherapy's awful side effects may lie with our gut microbes, early evidence suggests. As chemotherapy drugs are eliminated from the body, bacteria in the gastrointestinal tract can latch onto them and transform them into toxic species that cause severe diarrhea. In a Chemistry & Biology article published online on September 10, researchers present ways to shut down the ability of GI microbes to convert chemotherapy drugs to a toxic species in mice as a first step to helping cancer patients.
"The GI microbiota are the great crowd-sourcers of chemistry, ...
2015-09-10
Have you ever touched someone else and wondered why his or her skin felt so incredibly soft? Well, now researchers reporting in the Cell Press journal Current Biology on September 10 present evidence that this experience may often be an illusion.
In a series of studies led by Aikaterini Fotopoulou of the University College London, participants consistently rated the skin of another person as being softer than their own, whether or not it really was softer. The researchers suggest that this phenomenon may exist to ensure that humans are motivated to build social bonds ...
2015-09-10
Those of you who spend hours at the gym with the aim of burning as many calories as possible may be disappointed to learn that all the while your nervous system is subconsciously working against you. Researchers reporting in the Cell Press journal Current Biology on September 10 have found that our nervous systems are remarkably adept in changing the way we move so as to expend the least amount of energy possible. In other words, humans are wired for laziness.
The findings, which were made by studying the energetic costs of walking, likely apply to most of our movements, ...
2015-09-10
For patients and clinicians alike, it's long been a mystery: why do symptoms of multiple sclerosis (MS) seem to get better in the winter and worse in the summer? A group led by Francisco Quintana, PhD, at the Ann Romney Center for Neurologic Diseases at Brigham and Women's Hospital (BWH) and collaborators have found an explanation that could lead to a deeper understanding of the disease and more targeted treatment options for patients. By first looking broadly at possible environmental factors and then deeply at preclinical models of MS, the research team found that melatonin ...
LAST 30 PRESS RELEASES:
[Press-News.org] Megathrust quake faults weaker and less stressed than thought
