#foreshock

[khristofo-thegreat]

Earthquake explanation.

Yesterday's Earthquake (6.1) was a foreshock. A foreshock is an earthquake that occurs before the the mainshock.

The Earthquake tonight (7.1) was most likely the Mainshock unless this is also a foreshock for a bigger one.

The 5.4 was a aftershock of the foreshock. And most likey there will be another 5-6 magnitude aftershock in the next few days.

[energynews247]

New study models the transmission of foreshock waves towards Earth -- ScienceDaily

New study models the transmission of foreshock waves towards Earth — ScienceDaily

An international team of scientists led by Lucile Turc, an Academy Research Fellow at the University of Helsinki and supported by the International Space Science Institute in Bern has studied the propagation of electromagnetic waves in near-Earth space for three years. The team has studied the waves in the area where the solar wind collides with Earth’s magnetic field called foreshock region, and…

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[nuramalion]

Kejutan di Jumat pagi (Gempa PasamanBarat-25 Februari 2022)

Kejutan di Jumat pagi (Gempa PasamanBarat-25 Februari 2022)

Jum’at 25 Februari 2022 Pukul 08.30 Pagi ini cuaca Padang Panjang sedang cerah, waktu yang tepat untuk berjemur menyerap Vitami D dari alam. Meski begitu udara masih terasa dingin, saya berniat menunggu pancaran radiasi matahari sedikit lebih hangat sambil menyantap sarapan. Kamar kos saya berada di lantai dua, dengan pintu masuk di sebelah Barat dan Pintu menuju beranda di Sebelah Selatan.…

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[dailyvideovault]

New video posted on: https://dailyvideovault.com/7-1-magnitude-earthquake-strikes-southern-california/

7.1 magnitude earthquake strikes southern California

[twothumbsandnostakeincanon]

anyway when I named “Foreshock” I was like “man I’m so good at naming things, a foreshock precedes an earthquake, this fic starts with an earthquake and deals with Stiles having foresight/seeing the future, amazing, what a good name”

but

everytime I see it

my eyes don’t say 

Foreshock

they say

Foreskin

[earthstory]

The Holy Grail: Earthquake prediction

Whenever anyone asks about predicting earthquakes I generally feel that I am on shaky ground. I know more about the mechanics of materials, and I know that brittle fracture … breaking glass if you like, is inherently random. Trying to predict random events is like betting on the lottery. On average, it's a waste of time (/money). But that doesn't stop people trying. The risks associated with earthquakes are high, so the returns on being able to say something, no matter how little, seem high too.

In a paper just about to be published in Geophysics Research Letters, Chen and Shearer, at UC San Diego, demonstrate that there may be something to be learned from the foreshocks that are often seen just before major quakes. They have compared the foreshocks and aftershocks that were measured before and after three similar sized (M > 7) quakes on strike-slip faults adjacent to the main North America - Pacific plate boundary in California.

The foreshocks are not associated with significant stress drops, unlike the aftershocks. Chen and Shearer also find that the foreshock sequences sometimes separate into two periods, initially occurring over the entire foreshock region and then migrating toward the main shock location. It seems that the distribution of foreshocks reflects the complex pattern of minor faults within the fault zone. But the foreshocks do not increase in intensity or frequency before the main shock, implying they do not trigger it of themselves. And the three similar sized quakes do not have similar patterns of foreshocks, again suggesting that they are not the cause of the main event. Rather, it seems that both foreshocks and main shock are the result of an (unknown) external transient stress perturbation.

So, these foreshock sequences, swarms of small quakes, reflect an underlying trigger, but not always! Four such seismic bursts were recorded in the region studied between 1989 and 2002, and of the four, only two were followed by a main event. None the less, that seems to me to be quite a step forward in potentially characterising those foreshocks that might result in a significant quake.

~SATR

Image: San Andreas Fault on the Carrizo Plain, CA. The North American plate is to the east on the right, while on the left lies the Pacific plate. (creative commons, dsearls, Flickr)

Link: http://onlinelibrary.wiley.com/doi/10.1002/grl.50444/abstrac

[earthstory]

FORESHADOWING EARTHQUAKES: FORESHOCKS AND EARTHQUAKE PREPARATION

Many major earthquakes are often preceded by foreshocks. Foreshocks are smaller vibrations that occur prior to some highly destructive earthquakes. Because not every earthquake has accompanying foreshocks, scientists have found it challenging to use foreshocks as an earthquake prediction tool. A new study published in Nature Geoscience has revealed more information about these vibrations.

Earthquakes usually occur at plate boundaries. Some plate boundaries feature plates that slowly slide past each other over time. When the plates reach points along their boundaries where the rocks become stuck, pressure builds. According to the study, these areas eventually break under enough pressure from the slow movement and release foreshocks. Large, more violent earthquakes are produced when the break in the rock occurs more quickly.

North Pacific Ocean-based earthquakes larger than a magnitude of 6.5 that were generated at depths shallower than 50 kilometers, and occurring between 1999 and 2011, were analyzed. This region was chosen because Japan, Mexico, Taiwan and the United States have many instruments set up in this region designed for earthquake detection. Half of the 62 earthquakes studied occurred at plate boundaries with subduction zones (where one more dense plate slides beneath another less dense plate) and strike-slip faults (where plates slide past each other); the other half of the data came from intraplate earthquakes, which occur far away from plate boundaries.

About 20 days before a major earthquake, the researchers noted that the seismicity (earthquake distribution in a certain location over time) increased due to the presence of foreshocks. This increase in activity continued until a major earthquake occurred. There was no such predictable pattern of activity for intraplate earthquakes, since foreshocks here occurred much less frequently.

Foreshock events such as the ones examined in the Nature Geoscience study were noted prior to a major earthquake in Izmit, Turkey in 1999 that killed 17,000 people and left 500,000 homeless. According to a study published in Science, the magnitude 7.6 earthquake along the North Anatolian fault was preceded by bursts of seismic activity in the form of foreshocks that increased over time. The crust in the region had undergone a period of slow sliding for 44 minutes prior to the earthquake, generating the foreshocks. The sliding accelerated in the two minutes before the major earthquake occurred.

Foreshocks do not create larger earthquakes, but may help scientists to understand the process of earthquake generation. The prolonged activity generated by foreshocks preceding major earthquakes can help us to better prepare for potential earthquake events.

-Jeanne K.

Photo courtesy of Kyodo News/Associated Press. The photo depicts some of the damage incurred from the magnitude 9.0 Tohoku Earthquake and subsequent tsunami near the east coast of Honshu, Japan. Studying seismic zones such as this one for foreshocks could help scientists become more aware of potentially hazardous future earthquakes.

References: http://www.nature.com/ngeo/journal/v6/n4/full/ngeo1770.html#access

http://www.livescience.com/28134-earthquake-slow-slip-foreshocks-found.html

http://www.sciencemag.org/content/331/6019/877

http://www.ouramazingplanet.com/945-earthquakes-foreshocks-faults.html

http://earthquake.usgs.gov/earthquakes/eqinthenews/2011/usc0001xgp/#summary