The dominant rupture process theory implies that we can’t determine the earthquake magnitude from it’s rupture initiation. However, the new findings with the following paper suggest that we could determine the earthquake magnitude by studying the frequency content for the first few seconds of the rupture.
Please visit the paper by the following link:
http://www.nature.com/nature/journal/v438/n7065/abs/nature04214.html
Our beliefs are changing through time, because some of them had been chosen based on our world view and what can fit with our previous background rather than what can represent nature itself. However, one of those beliefs is about earth’s inner core structure and iron crystals orenintation. Geoscientists used to represent the inner core as a cylindrical symmetry that aligned towards the poles (north-south). In fact, they had no evidence for that except that it fit their general model for the earth interior.
Recently, a group of scientists studied carefullay the seismic waves that penetrate the inner core and tried to discover the iron crystal orientation. The results were astonished when they found two orientations within the inner core. The inner part of the inner core shows iron crystal alinement toward the equator while the outer part of the inner core is almost perpendicular in which it shows north-south alinement. What can such finding tell us about Earth? In fact, that would improves our understanding about how our planet from in one hand, and give an important insight about inner core dynamics in the other hand.
Please visit the following link for more details:
http://sk8es4mc2l.search.serialssolutions.com/?ctx_ver=Z39.88-2004&ctx_enc=info%3Aofi%2Fenc%3AUTF-8&rfr_id=info:sid/summon.serialssolutions.com&rft_val_fmt=info:ofi/fmt:kev:mtx:journal&rft.genre=article&rft.atitle=Equatorial+anisotropy+in+the+inner+part+of+Earth%27s+inner+core+from+autocorrelation+of+earthquake+coda&rft.jtitle=NATURE+GEOSCIENCE&rft.au=Wang%2C+T&rft.au=Song%2C+XD&rft.au=Xia%2C+HH&rft.date=2015-03-01&rft.pub=NATURE+PUBLISHING+GROUP&rft.issn=1752-0894&rft.eissn=1752-0908&rft.volume=8&rft.issue=3&rft.spage=224&rft.epage=227&rft_id=info:doi/10.1038%2FNGEO2354&rft.externalDBID=n%2Fa&rft.externalDocID=000350770900022¶mdict=en-US
As science is defined by philosphers as the procces of discovering patterns, however, sometimes those patterns break down revealing new exception! In fact, with time those exceptions form a new pattern.
In lithospheric dynamics, is well known that earthquakes occure in the brittle part of the crust, while creep occurs in ductile part of crust. That is not the case in Hollister in California where creep can be found on the surface!! However, geoscientists have different explinations for such phenomena. Check the following link which is a report made by USGS summerized most of the geophysical findings in Calaveas fault creep in Hollister.
http://search.proquest.com.ezaccess.libraries.psu.edu/docview/1641132558?pq-origsite=summon
As we finishing the semester, I thought about having a list about the most difficult challenges in seismology based on what we have learned so far. The following pdf file represents a national report that combined a couple of question that seismologists could not answer yet. In my opinion this is good way to think about what is unknown in seismology and earth dynamics as well.
The Nepal earthquake and it’s enormous aftershocks inspired again my thoughts about earthquake triggering. However, being involved in such class gave a basic understanding of how earthquakes works, hence I started searching for an earthquake model that enables such phenomena without a huge number of assumptions.
Most recently, there was a paper published in the journal of Physics of the Earth and Planetary Interiors, that entitled “Dynamic triggering of earthquakes is promoted by crustal heterogeneities and bimaterial faults”. The take away point of this paper is that both stiff and weak materials focus stress waves to form an enhanced stress zone. However, their work provided a non-uniform of such zone in a heterogeneous medium.
Find the paper over the following link:
On May 24th, 2013 the largest known deep earthquake (~600 km) with Mw 8.3 occurred beneath the Okhotsk sea. Such an event may reshape our understanding of deep earthquakes. I don’t know many details about the nature of deep earthquakes, I’m wondering if the mineralogical phase change associated with the 660-km discontinuity could contribute to these deep events? The more generally accepted explanation for deep earthquakes is nucleation by a phase transition within the subducted material, for example:
http://earthquake.usgs.gov/earthquakes/eqarchives/poster/2013/20130524.pdf
One interesting thing I found in the poster is that the shaking intensity distribution shows an interesting pattern. Can we use it to learn about the earth structure above the source?
The 2010 Haiti earthquake has been considered as a result of a rupture that initiated on a small subsidiary fault and the rupture transitioned into larger even, but did not initiate slip on an even larger nearby structure. However, this is not the case all the time, where most of ruptures that initiated in small fault don’t transfer their energy into larger ruptures. It’s obvious that seismologists are struggling with such issue, neverthless, my question is what is the key that we should know to solve the problem?
I recommand you to check this paper:
http://onlinelibrary.wiley.com.ezaccess.libraries.psu.edu/doi/10.1002/2014JB011595/abstract
Thamer
The authors describe their use of off-shore observations to demonstrate the existence of splay faulting in the shallow regions of the Chilean Subduction Zone involved in the Mw 8.8, 2010 Maule, Chile earthquake. A splay fault is a relatively steep fault that connects the plate boundary interface with the seafloor that when activated during a large earthquake, can enhance tsunami excitation. Based on previous work noted in the paper, the most likely location of splay faults is along the boundary between outer and inner wedges, which is where the authors, Liessr and others, observed the seismic activity in the Chile study.
Specifically, the authors deployed a 30-station ocean-bottom seismometer network for three months and analyzed the offshore data in concert with observations from another 33 land-based seismic stations. They used a a 2.5 dimensional velocity model derived from seismic reflections profiles and previous local earthquake studies to locate the aftershocks.
Good data coverage provides a road to good results, which in this case includes several interesting outcomes. The aftershock locations illuminate a 50 km long linear structure extending from the plate boundary interface to the seafloor that coincides with a splay fault outcrop (on top of the wedge). The P-wave speed distribution (estimated from active-source and tomographic results) suggests that the splay fault begun to branch off with an angle of 7⁰-8⁰ from the plate boundary interface at ~20 km depth and ~67 km away from the deformation front. Finally, it’s important to mention that the southern part of the study area it does not appear that the main shock experienced any activity associated with a splay fault.
Please see the papers for details: http://geology.gsapubs.org/content/41/12/e309.full
Thamer
The WSM is a project that established to provide a data base for the stress distribution in the world. However, they have different techniques to calculate stress magnitude and orientation. One of those techniques is the earthquake mechanism based on either P-wave polarity analysis or moment tensor analysis. In the both methods we can’t determine fault plane from auxiliary plane.
The WSM has couple of categories that describe the data quality. For example, they consider the stress that extracted from borehole data has higher quality than the one extracted from earthquake analysis. That because it’s not necessary that fault failure in earthquakes will indicates to the regional stress pattern. For example, having salt will change the local stress orientation from the regional one in which if failure occured the earthquake setting will nor showing the stress major trend in the area.
For more datails about WSM project visit the following link.