Recent comments in /f/askscience

GeriatricHydralisk t1_j7p82qz wrote

Tendons heal and remodel slowly simply because they're mostly collagen with very few cells, compared to muscle (almost all cells) and bone (which has a surprisingly high number of cells). Even with every cell working flat-out to fix/alter the tendon, there's just soooo much collagen and so few cells that it takes forever.

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CrustalTrudger t1_j7p4jnd wrote

> and deduce that every X amount of years the Cascadia Subduction Zone ruptures with some regularity.

I guess this depends on your definition of "regular." If you look a the intervals between events reconstructed from the turbidite record (Table 12 on page 115 of Goldfinger et al., 2012), you'll see that these aren't exactly evenly spaced. E.g., the spacing in years between events is 232, 316, 446, 311, 982, 492, 415, 665, 661, 1189, 508, 715, 443, 548, 733, 195, 117, 577. From this you can calculate an average and it tells you that generally you'd expect an event every few hundred years, but after a given event, there's not necessarily anything to indicate whether the next one is going to be in ~100 years or ~1000 years. I would not describe that as having a particularly "regular" pattern of strain release.

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doucheluftwaffle t1_j7ozgpr wrote

OP- the small little quakes that we have in the PNW don’t occur on/in the cascadia subduction zone.

The little earthquakes that we have are a result of us being pushed north by the San Andreas Fault. Assuming you’re in WA state, the further north you go towards Bellingham, the geology up there is mostly granite. So when we’re pushed northward, there’s no where for us to go except into the granite and lala you get the occasional low magnitude earthquake.

On land are major faults are strike slip and thrust faults and not subduction. Those faults aren’t going to help relieve Cascadia nor are they foreshocks to “The Big One.” The quakes on these faults are from normal movement and occasionally they get stuck.

As for being overdue- it’s nearly impossible to predict when Cascadia will rupture. However, geologists can study the sediment layers on the coast along with the ghost forests. Look up WA coast ghost forest; it’s really fascinating. They can also look at Native American Legends along with the written records in Japan and deduce that every X amount of years the Cascadia Subduction Zone ruptures with some regularity.

Typically scientists cant say with certainty whether or not an earthquake is a foreshock. Its only after a big one can they say that the previous one was likely a foreshock. For example; in 2002 Sumatra had 7.3 quake and then in 2004 they had a 9.1. It was only after the 9.1 did they say that the 2002 7.3 was a foreshock; separated by 2 years.

If you look at the Tohoku Japan quake (Fukushima) on they had 2 foreshocks; a 7.3 on 3/9/2011 and a 6.4 on 3/10/2011. Then on 3/11/2011 they had a 9.1.

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CrustalTrudger t1_j7oz7j4 wrote

A "local" scale is specifically calibrated so that some measurable quantity (like the amplitude of seismic waves as measured on a seismometer) gives a somewhat repeatable estimate of earthquake size, but only for a specific area. This is because local scales, like the Richter scale, are effectively a measure of ground shaking. For a given magnitude of earthquake (in the moment magnitude sense, which is a measure of an intrinsic property of the earthquake, i.e., the seismic moment), the details of ground shaking will depend on distance/depth but also details of the rock that the seismic waves passed through between the source and the seismometer. So for the Richter scale and other local magnitude scales, if you try to transport it somewhere else, the magnitude won't be equivalent. I.e., a true Richter magnitude of X in one place won't actually be the same size earthquake of a Richter magnitude of X earthquake somewhere else. That's not a a very useful property for a scale to have.

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CrustalTrudger t1_j7oybui wrote

To clarify, the media isn't using the Richter scale, the media is reporting what ever magnitude a given service (e.g., the USGS or GFZ Potsdam GEOFON, etc) reports and then calling it a "Richter" magnitude. That magnitude is typically a moment magnitude, but depending on the location and details, it might be one of several seismic magnitude scales, e.g., occasionally you'll see a body wave magnitude (mb) or a surface wave magnitude (Ms) reported for a particular earthquake. As to why calling everything a "Richter" magnitude has persisted, it's unclear. The Richter scale was the first, but it was always a local scale (i.e., it was only really calibrated to be used in one part of the world) and it hasn't effectively been used for >50 years.

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