# 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.

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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: 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: 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