# gst: continuous, (not intermittent, perpetual) tremors and slips ...

<< Applying deep learning to seismic data has revealed tremor and slip occur at all times—before and after known large-scale slow-slip earthquakes—rather than intermittently in discrete bursts, as previously believed. Even more surprisingly, the machine learning generalizes to other tectonic environments, including the San Andreas Fault. >>

Machine learning reveals earth tremor and slip occur continuously, not intermittently. Los Alamos National Laboratory.  Feb 27, 2020.

https://m.phys.org/news/2020-02-machine-reveals-earth-tremor-intermittently.html

<< Slow earthquakes cyclically load fault zones and have been observed preceding major earthquakes on continental faults as well as subduction zones. Slow earthquakes and associated tremor are common to most subduction zones, taking place downdip from the neighboring locked zone where megathrust earthquakes occur. In the clearest cases, tremor is observed in discrete bursts that are identified from multiple seismic stations. By training a convolutional neural network to recognize known tremor on a single station in Cascadia, we detect weak tremor preceding and following known larger slow earthquakes, the detection rate of these weak tremors approximates the slow slip rate at all times, and the same model is able to recognize tremor from different tectonic environments with no further training. >>

Bertrand Rouet-Leduc, Claudia Hulbert, et al. Probing Slow Earthquakes With Deep Learning. Geophysical Research Letters. Volume 47, Issue 4. doi: 10.1029/2019GL085870. Jan 23, 2020.

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019GL085870

# gst: triggering earthquakes, even the slightest stress can set off a tremor

<< A new study reveals the inner workings of tidally triggered earthquakes, and finds that even the slightest stress can set off a tremor. >>

Solved: How tides can trigger earthquakes. Earth Institute At  Columbia University. Jun 7, 2019.

https://www.eurekalert.org/pub_releases/2019-06/eiac-sht060519.php

<< The strong tidal triggering of mid-ocean ridge earthquakes has remained unexplained because the earthquakes occur preferentially during low tide, when normal faulting earthquakes should be inhibited. >>

AA << show that the axial magma chamber inflates/deflates in response to tidal stresses, producing Coulomb stresses on the faults that are opposite in sign to those produced by the tides. When the magma chamber’s bulk modulus is sufficiently low, the phase of tidal triggering is inverted. >>

Christopher H. Scholz, Yen Joe Tan, Fabien Albino. The mechanism of tidal triggering of earthquakes at mid-ocean ridges. Nature Communications 10, Article number: 2526 June 7, 2019.

https://www.nature.com/articles/s41467-019-10605-2

# gst: a slow motion can triggers strong, fast-slip (many miles away)

<< At a glacier near the South Pole, earth scientists have found evidence of a quiet, slow-motion fault slip that triggers strong, fast-slip earthquakes many miles away,  >>

<< During an earthquake, a fast slip happens when energy builds up underground and is released quickly along a fault. Blocks of earth rapidly slide against one another. However, at an Antarctic glacier called Whillans Ice Plain, (they) show that "slow slips" precede dozens of large magnitude 7 earthquakes. >>

<< We found that there is almost always a precursory 'slow slip' before an earthquake, >> Grace Barcheck.

<< these slow-slip precursors- occurring as far as 20 miles away from the epicenter- are directly involved in starting the earthquake. >>

<< These slow slips are remarkably common, (..) and they migrate toward where the fast earthquake slip starts. >>

<< Within a period of two months in 2014, the group captured 75 earthquakes at the bottom of the Antarctic glacier. Data from GPS stations indicated that 73- or 96% - of the 75 earthquakes showed a period of precursory slow motion. >>

Blaine Friedlander. Slow motion precursors give earthquakes the fast slip. Cornell University. Feb 16, 2021.

️

https://phys.org/news/2021-02-motion-precursors-earthquakes-fast.html

G. Barcheck, E. Brodsky, et al. Migratory earthquake precursors are dominant on an ice stream fault. Science Advances. Vol. 7, no. 6, eabd0105. doi: 10.1126/ sciadv.abd0105. Feb 5, 2021.

https://advances.sciencemag.org/content/7/6/eabd0105  

# gst: detect and monitor a deep tremor

<< “Deep tremor is very sensitive to small stress changes,” Chao [Kevin Chao] said. “So, we decided to use them as stress meters to monitor local variations in stress build-up and release before and after large earthquakes” >>

Amanda Morris. Do Earthquakes Have a ‘Tell’? Data scientists and seismologists use “deep tremor” to forecast strong earthquakes. Oct 5, 2017.

http://www.mccormick.northwestern.edu/news/articles/2017/10/do-earthquakes-have-a-tell.html

https://www.sciencedaily.com/releases/2017/10/171005151119.htm

Kevin Chao, Zhigang Peng, et al.
Temporal variation of tectonic tremor activity in southern Taiwan around the 2010 ML6.4 Jiashian earthquake. Journal of Geophysical Research: Solid Earth. 2017; 122(7): 5417–34 doi: 10.1002/2016JB013925

http://onlinelibrary.wiley.com/doi/10.1002/2016JB013925/abstract

also

http://flashontrack.blogspot.it/search?q=earthquakes

# s-gst: unexpected silent zones in interseismic period, a long-standing enigma ...

<< Why  many  major  strike-slip  faults  known  to  have  had  large  earthquakes  are  silent  in  the interseismic  period  is  a  long-standing  enigma.  One  would  expect  small  earthquakes  to  occur  at least  at  the  bottom  of  the  seismogenic  zone,  where  deeper  aseismic  deformation  concentrates loading.  [AA]  suggest  that  the  absence  of  such  concentrated  microseismicity  indicates  deep rupture  past  the  seismogenic  zone  in  previous  large  earthquakes >>

Bob Yirka. New  theory  to  explain  why  some  fault  segments remain  quiet  between  quakes.  June 10, 2016.

http://m.phys.org/news/2016-06-theory-fault-segments-quiet-quakes.html

Junle Jiang , Nadia Lapusta. Deeper  penetration  of  large  earthquakes  on  seismically  quiescent  faults. Science    10  Jun  2016: Vol.  352,  Issue  6291,  pp.  1293-1297 DOI:10.1126/science.aaf1496.

http://dx.doi.org/10.1126/science.aaf1496

FonT: quando una decina di giorni fa ho letto questa news, chissa' perche', ho pensato a BRexit ...

BRexit:   http://www.bbc.com/news/politics/eu_referendum/results

# s-behav: the intricate performance (dancing and singing) of a jumping spider

AA << present behavioral and neurophysiological evidence that [Jumping spiders (Salticidae)]  perceive and respond to airborne acoustic stimuli, even when the distance between the animal and the sound source is relatively large (∼3 m) and with stimulus amplitudes at the position of the spider of ∼65 dB sound pressure level (SPL) >>

<< Behavioral experiments with the jumping spider Phidippus audax reveal that these animals respond to low-frequency sounds (80 Hz; 65 dB SPL) by freezing—a common anti-predatory behavior characteristic of an acoustic startle response >>

<< Neurophysiological recordings from auditory-sensitive neural units in the brains of these jumping spiders showed responses to low-frequency tones (80 Hz at ∼65 dB SPL)—recordings that also represent the first record of acoustically responsive neural units in the jumping spider brain.  Responses persisted even when the distances between spider and stimulus source exceeded 3 m and under anechoic conditions. >>

Paul S. Shamble, Gil Menda, et al.
Airborne Acoustic Perception by a Jumping Spider. Current Biology. DOI: 10.1016/j.cub.2016.08.041 Publ. Oct. 13, 2016

http://www.cell.com/current-biology/fulltext/S0960-9822(16)30985-X

Jaymi Heimbuch. Jumping spider males dance and sing ... Oct. 4, 2016.

http://www.mnn.com/earth-matters/animals/stories/jumping-spider-males-dance-and-sing-yes-sing-woo-their-mates

FonT: sarebbe interessante valutare se e quanto tempo prima la struttura neuroacustica del Phidippus audax sia in grado di percepire e discriminare le basse freq dei movimenti  tellurici profondi che successivamente manifesteranno  macro episodi di superficie (earthquake).

also:

Richard A. Lovett. Scientists Seek Foolproof Signal to Predict Earthquakes. National Geographic News. Jan. 5, 2013

http://news.nationalgeographic.com/news/2013/01/04-earthquakees-defy-prediction-efforts/

Vanessa Bates Ramirez. Earthquakes Will Be as Predictable as Hurricanes Thanks to AI. Sep 27, 2016

http://singularityhub.com/2016/09/27/earthquakes-will-be-as-predictable-as-hurricanes-thanks-to-ai

# gst: early seismic waves could allow to glimpse the power of the main temblor

AA << explore databases of earthquake source time functions and find that they are composed of distinct peaks that (..) call subevents (..) the main event magnitude can be estimated after observing only the first few subevents. >>

Philippe Danre, Jiuxun Yin, et al. Earthquakes Within Earthquakes: Patterns in Rupture Complexity. Geophysical Research Letters. Volume 46, Issue 13. doi: 10.1029/ 2019GL083093. Jun 25, 2019.   https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL083093

Anna Fiorentino. Early seismic waves hold the clue to the power of the main temblor. Harvard University. Aug 8, 2019.  https://m.phys.org/news/2019-08-early-seismic-clue-power-main.html  

# gst: temblors with a 'boomerang' effect

<< The temblor shot eastward across a deep gash in the seafloor, and then zipped back to where it started at incredible speeds. It moved so fast it created the geologic version of a sonic boom. >>

Maya Wei-Haas. Weird ‘boomerang’ earthquake detected under the Atlantic Ocean. Aug 10, 2020.

https://www.nationalgeographic.com/science/2020/08/weird-boomerang-earthquake-detected-under-atlantic-ocean/   

AA << present an analysis of the 2016 Mw 7.1 earthquake on the Romanche fracture zone in the equatorial Atlantic, (..) (They) show that this rupture had two phases: (1) upward and eastward propagation towards a weaker region where the transform fault intersects the mid-ocean ridge, and then (2) an unusual back-propagation westwards at a supershear speed towards the centre of the fault. (..) deep rupture into weak fault segments facilitated greater seismic slip on shallow locked zones. This highlights that even earthquakes along a single distinct fault zone can be highly dynamic. Observations of back-propagating ruptures are sparse, and the possibility of reverse propagation is largely absent in rupture simulations and unaccounted for in hazard assessments. >>

Hicks, S.P., Okuwaki, R., et al. Back-propagating supershear rupture in the 2016 Mw 7.1 Romanche transform fault earthquake. Nat. Geosci. (2020). doi: 10.1038/ s41561-020-0619-9. Aug 10, 2020.

https://www.nature.com/articles/s41561-020-0619-9 

# gst: to estimate a minimum size of an earthquake

<< Although the overall size of an earthquake cannot be predicted from the rate of energy release, a minimum size can be estimated. Estimating this minimum size could add valuable seconds to early earthquake warning algorithms >>

M.A. Meier, J. P. Ampuero, T. H. Heaton. The hidden simplicity of subduction megathrust earthquakes.  Science Sep 22,  2017: 357 (6357): 1277-81. doi: 10.1126/science.aan5643

http://science.sciencemag.org/content/357/6357/1277

# gst: the 'memory' of a friction

<< Contrary to what you may have learned in high school, friction between two surfaces is not constant. For a wide range of materials and surface types, it increases with time, as microscopically uneven surfaces deform and come into closer contact. Experiments now find an additional wrinkle: friction can have a memory, meaning that it can depend not only on the current state of the interface but also on how it got there. The findings hint at connections between friction and the behavior of glasses and other disordered systems and, in the long run, may influence how scientists think about friction associated with earthquakes, industrial machinery, and micromachines. >>

David Lindley. Focus: Friction Remembers Its Origins. Physics 11, 55. Jun 1, 2018

https://physics.aps.org/articles/v11/55

# geo gst: even small flank failures can cause large tsunamis

<< Volcanogenic tsunamis are one of the deadliest volcanic phenomena. >>

<< Small flank failures causing large tsunamis represent a vastly underappreciated geohazards-current tsunami monitoring systems do not monitor for this kind of volcanic activity, instead focusing on large earthquakes or proxies related to unusual increases in magma intrusion.  >>

<< This collapse was captured in unprecedented detail by satellite remote sensing, providing an opportunity to understand the collapse of the volcano (Anak Krakatau volcano,  Indonesia) in a way that has not previously been possible at any volcanic island in the world. >>

Reconstructing the Anak Krakatau flank collapse that caused the December 2018 Indonesian tsunami. Geological Society of America. Aug 30, 2019.   https://m.phys.org/news/2019-08-reconstructing-anak-krakatau-flank-collapse.html   

<< the volume of material initially lost from the volcano flank failure (..) was relatively small (~0.1 km3) compared to the overall changes observed during the entire eruption, but it was nonetheless able to generate rapid tsunami waves with devastating impacts. The flank failure also changed the eruption style and the upper volcanic plumbing system, with the subsequent explosive eruptions destroying the summit and then partially rebuilding the lost flank.  >>

Rebecca Williams, Pete Rowley, Matthew C. Garthwaite. Reconstructing the Anak Krakatau flank collapse that caused the December 2018 Indonesian tsunami. Geology. doi.org/10.1130/G46517.1. Aug 30, 2019.    https://pubs.geoscienceworld.org/gsa/geology/article-abstract/573356/reconstructing-the-anak-krakatau-flank-collapse