Posted on 11/21/2021 10:08:48 PM PST by BenLurkin
Geologists have measured a devastating 'four-leaf clover' pattern of earthquake shockwaves in greater detail than ever before – and the resulting findings could be crucial in making our buildings and cities more resistant to large quakes in the future.
This four-pronged pattern has been analyzed before, but never in as much depth as this. The team behind the new study is hoping that it might remove some of the mystery surrounding how earthquake shockwaves spread out across different frequencies.
Crucially, the cloverleaf shockwaves spread at low frequencies of under 10 hertz, a level of vibration that many buildings and structures are particularly vulnerable to.
The researchers looked at data from one of the densest seismic arrays on the planet: the LArge-n Seismic Survey in Oklahoma (LASSO), which is made up of 1,829 seismic sensors within an area of just 15 by 20 miles (25 by 32 kilometers).
LASSO was used to measure P-wave data from 24 small earthquakes across a period of 28 days in 2016, and it's this data that the new study digs into. Having sensors so close to the epicenter of the quakes meant that patterns could be spotted before they smoothed out and evened off over greater distances.
By using algorithms to filter shockwaves by frequency, the four-leaf clover pattern emerged, but only at the lower frequencies. That might be because lower frequency seismic waves can bypass the jumble of broken rock found at earthquake faults, rather than being reflected and scattered in many different directions.
(Excerpt) Read more at sciencealert.com ...
May need to read it again, but is there an explain why the shock pattern is a quadrapole pattern rather than an isotropic source/omnidirectional?
Not like slippages are in an array to form such a pattern.
Read one of the linked articles, sounds like they do not understand the pattern, it just is.
I don’t understand any of it.
If earthquakes are the result of fault line slips can it be that the four directions are along the fault line and perpendicular to it? Or could it be the result of interference patterns caused by waves adding in phase or cancelling when out of phase
The only way I can think of that would result in that quadripolar-like pattern is for two intersecting fault lines to both have shifts/slippage, both happening at roughly the same time.
figure 8 actual transmission with side lobes ss the hatmonics.
similar to radio frequency transmission patterns.
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