Earthquakes do occur in Antarctica, but not very often. There have been some big earthquakes--including one magnitude 8 --in the Balleny Islands between Antarctica and New Zealand. The boundary between the Scotia Plate and the Antarctic Plate just grazes the north tip of the Antarctic Peninsula look "northwest" from the Pole toward South Where can I find earthquake educational materials? Start with our Earthquake Hazards Education site. Can we cause earthquakes? Is there any way to prevent earthquakes?
Earthquakes induced by human activity have been documented at many locations in the United States and in many other countries around the world. Earthquakes can be induced by a wide range of causes including impoundment of reservoirs, surface and underground mining, withdrawal of fluids and gas from the subsurface, and injection of fluids into What is surface faulting or surface rupture in an earthquake? Surface rupture occurs when movement on a fault deep within the earth breaks through to the surface.
At what depth do earthquakes occur? What is the significance of the depth? Earthquakes occur in the crust or upper mantle , which ranges from the earth's surface to about kilometers deep about miles. The strength of shaking from an earthquake diminishes with increasing distance from the earthquake's source, so the strength of shaking at the surface from an earthquake that occurs at km deep is considerably Why are there so many earthquakes in the Geysers area in Northern California?
The major seismic hazards in the region are from large earthquakes occurring along regional faults that are located miles away from the geothermal field, such as the San Andreas and Healdsburg-Rodgers Creek faults.
However, activities associated with What is an earthquake and what causes them to happen? An earthquake is caused by a sudden slip on a fault. The tectonic plates are always slowly moving, but they get stuck at their edges due to friction. When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the earth's crust and cause the shaking that we feel.
In California there Can the position of the moon or the planets affect seismicity? Earthquakes are equally as likely to occur in the morning or the evening. Many studies in the past have shown no significant correlations between the rate of earthquake occurrence and the semi-diurnal tides when using large earthquake catalogs. Several recent studies, however, have found a correlation between earth tides caused by the position of Filter Total Items: Wald, Lisa A.
View Citation. For example, the number of aftershock will decrease to one-tenth in the first 10 days, whereas it will only decrease to one-half in the next 10 days. This is the reason why we feel like the aftershock lasts for a long time. In addition, the larger the magnitude of the main-shock is, the longer it takes for the aftershock to settle. Frequency of aftershocks differs according to their magnitudes.
For instance, the number of aftershocks with magnitude of 5 is about 10 times larger than that of aftershocks with magnitude of 6. Ed Yong says ,. In other words, there's not a lot going on that would show at the surface, unlike the San Andreas, which is bleeding obvious.
New Madrid is a slow, sleepy fault, despite the excitement it caused over the winter of Compared to New Madrid, the San Andreas fault is a speed demon, and it shows. There are other differences, of course — one's a transform fault where two plates are scooting past each other, the other's more of a rift type thing where North America started splitting apart, then decided to stay together — but the main thing is speed.
According to the study, San Andreas locks and loads within a decade or so, leaving the aftershocks in the dust and nervous Californians waiting for the Big One. New Madrid's still squirming around trying to get comfortable after a fairly dramatic disruption.
And every time it twitches noticeably, folks in the Midwest get twitchy themselves. The river did, after all, run backwards the last time this thing went crack. Bound to worry folks a bit. But according to Stein and Liu, there's nothing much to worry about — at least, not where New Madrid's concerned. You're just in for hundreds of years of aftershocks, since the fault moves more than times slower than the San Andreas.
This is good news. And the data are beautiful :. And this study points to the fact that the small isn't always a foreshadow of the big :. Sounds like a very good idea to me. Anything we can do to increase the chances of successful earthquake prediction could help save a lot of lives.
And it allows us to rest easier when we find out that those little temblors are just past earthquakes saying "So long, and thanks for all the fish. The views expressed are those of the author s and are not necessarily those of Scientific American. A confirmed adorer of the good science of rock-breaking, Dana Hunter explores geology with an emphasis on volcanic processes, geology news, and the intersection of science and society.
Spatial distribution of the P-axis azimuths in the focal mechanism solutions. The colors of the P-axes indicate the classification of the focal mechanism type according to Frohlich , as defined by the color palette at top right. Since surface faulting was not emerged above the aftershock region of the Western Tottori Earthquake Ueta et al.
We applied principal component analysis PCA Shearer et al. In this analysis, the eigenvalues and eigenvectors of the covariance matrices in the x E—W , y N—S , and z depth coordinates of the hypocenter locations with respect to their mean locations were calculated.
We defined a hypocenter distribution with a planarity greater than or equal to 8 as a planar distribution, following the criterion in Shearer et al. For the planar distribution, the strike and dip angles of the best-fit plane were calculated using eigenvectors.
The selection of events for PCA was followed by these steps. First, we divided the aftershock region into the northern and southern parts Fig. Then, we conducted PCA for the hypocenter data in each part.
If the result meets the following three conditions, we estimated the best-fit fault plane for the region: 1 Planarity of the hypocenter distribution is greater than or equal to 8. If the result did not meet the first or second conditions, we divided the region into smaller parts based on the hypocenter distribution and conducted PCA for each small region again to obtain as many fault planes as possible. This procedure was repeated 4 times, assuming that the subsurface fault structure is simple.
The spatial division for event selection in each step and the results of PCA are shown in Additional file 1. We assumed that the best-fit planes define the position and orientation of the subsurface fault structure. Numbers correspond to the index numbers of faults listed in Table 1.
Figure 5 shows an example of the hypocenter distribution around the best-fit plane in the southern and northern parts of the aftershock region. The width and length of the best-fit plane were estimated from an edge of the hypocenter distribution projected onto the best-fit plane middle diagram in Fig. The event location projected onto the shortest axis x -axis of right-hand diagram in Fig. In order to evaluate the variety of focal mechanisms, we define a reference focal mechanism based on the orientation of best-fit plane.
The strike and dip angles of the reference focal mechanism were assumed to be those of the best-fit plane Table 1. The rake angle of the reference focal mechanism was assumed to be parallel to the resolved shear stress direction on the best-fit plane under the stress field reported by Yukutake et al. Hypocenter distribution around the best-fit planes. Left Hypocenter distribution along the strike of the best-fit plane.
The vertical and horizontal axes indicate, respectively, the directions along and normal to the best-fit plane. Middle and right Hypocenter distributions projected onto and perpendicular to the best-fit fault plane, respectively. Top Hypocenter distribution around Fault 1 middle that around Fault 2 and bottom that around Fault 8 in Fig.
The best-fit planes in this region Faults 1 and 2 are consistent with the orientation of one of the nodal planes in the CMT solution of the mainshock e. A large slip of more than 2 m occurred on Fault 1 during the mainshock Fig.
On the other hand, in the northern part of the aftershock region, a complicated spatial distribution of the aftershocks was estimated. The hypocenter distribution of the aftershocks suggests the existence of a conjugate fault system and is divided into several small clusters. The complicated structures of the best-fit plane were estimated Faults 5 through 8. Figure 6 shows the frequency distribution of the distance from the best-fit plane to each aftershock location. The aftershocks were concentrated on the best-fit plane, and the concentration decreased with the distance from the best-fit plane.
Figure 7 shows a histogram of A t around the 8 best-fit planes. The aftershocks around Faults 1 through 4 are distributed with zones of 1. Histograms showing the distance from the best-fit fault planes and the Kagan angles. Left The distance from the best-fit fault plane to each location of an aftershock. Right The Kagan angles from the reference focal mechanism. The Y -axis is normalized by the total number of events.
Some examples of focal mechanisms around Fault 1 at the Kagan angle are also shown in a. Histograms showing A t. The solid and open bins indicate, respectively, A t with a planarity greater than or equal to 8 and A t with a planarity less than 8. Most of the focal mechanisms are of the strike-slip type. These features of the focal mechanisms are consistent with those reported in previous studies e. We also evaluated the variety of the focal mechanisms based on the Kagan angle from the reference focal mechanism.
These results imply that the aftershocks do not occur on a simple plane. Figure 8 a shows the relationship between the hypocenter distance from Fault 1 or 2 and the Kagan angle from the reference focal mechanism. Most nodal planes of these focal mechanisms are oriented obliquely with respect to each best-fit plane rather than coincident with it.
Characteristics of the focal mechanisms around the mainshock fault. We selected the nodal plane for which the strike is closer to that of the best-fit plane. The thick black line indicates the strike of the best-fit plane. The red and gray lines indicate nodal planes of strike-slip type and other types, respectively. Note that the vertical and horizontal axes , respectively, indicate the directions along and normal to the best-fit plane.
The general features of the fault model obtained in the present study are consistent with those reported by Fukuyama et al. However, the locations of the best-fit planes in the northern part of the aftershock region were estimated at shallower depths compared with their fault model. This difference results from the uncertainty of the hypocenter depth in their study due to a lack of seismic stations above the northern part of the aftershock region.
According to the result of Sagiya et al. Based on these results, seismic slip during the mainshock is inferred to have occurred on Faults 1 through 4. The conjugate fault plane of Fault 4 was estimated at the northern edge of the mainshock fault.
Shibutani et al. A high-velocity structure corresponding to plutonic and metamorphic rocks was estimated along the mainshock fault in the southern part of aftershock region , whereas the northern part of the aftershock region was composed primarily of non-alkali volcanic and pyroclastic rocks of the early to middle Miocene, which are characteristic of a low-velocity zone.
The characteristics of fault structures appear to differ at this velocity boundary. A complicated fault system developed on the northern side, whereas a larger fault structure on the order of 10 km in length existed on the southern side Fig. The dynamic rupture process of the Western Tottori Earthquake was probably controlled by these pre-existing fault structures around the source region.
The aftershocks are distributed within approximately 1. Location errors of hypocenters in the horizontal direction strongly affect A t for a nearly vertical dipping fault plane, as observed in the study region. However, the estimated thickness cannot be explained by the location errors of the hypocenter in the horizontal direction that are less than 30 m for differential arrival time data obtained by both catalog and cross-correlation analysis.
There is also a possibility that the wide aftershock distribution around the mainshock fault results from a local irregularity in the mainshock fault geometry.
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