[conspire] Did you guys feel the 4.2 earthquake today?

[Rick Moen]

Quoting Steve Litt (slitt at troubleshooters.com), from the middle of last
week:

> Did you guys feel the 4.2 earthquake today?

(Downgraded after some approximate very early reports to 4.1.)

Here in West Menlo Park, no.  Isleton is a little-bitty town on the
Sacramento River about 120 miles NE of here, and a 4.1/4.2 is so minor
that it would have been perceivable only locally, over there, in the
Delta.

I know you used to live in (the other) California, Steve, so you
probably have some intuitive understanding of earthquake sizes, but the
general public that lives outside Earthquake Country are notorious for 
overestimating the small ones.

With a 4.1, there might have been as many as one teacup knocked off a
table in the next town over, Rio Vista.

USGS guidance for Mw (moment magnitude aka modified-Richter scale)
quakes of 4.0 - 4.9 is:

  Noticeable shaking of indoor objects and rattling noises.  Felt by
  most people in the affected area.  Slightly felt outside.  Generally
  causes zero to minimal damage.  Moderate to significant damage is very
  unlikely.  Some objects may fall off shelves or be knocked over.

Rio Vista would have been in "the affected area".  Sacramento was not,
and the S.F. Bay Area assuredly was not.

As you went through the "Northridge" (Reseda) Mw 6.7 quake, you know what a
real quake is like, though.  Anyway:  logarithmic scaling.  Non-intuitive.

Obligatory earthquake-culture joke, courtesy of Joss Whedon:
https://www.youtube.com/watch?v=AW1ji85MYEU   (cut to opening credits)
That was near the end of first-season Buffy.

I howled when I watched that scene, having, not too many years before,
gone through the quintessential California quake experience:  I'd been
sitting at a table outside the Bear's Lair pub on the UC Berkeley
campus, and an earthquake started.  Several people, inferred to be Not
>From Around Here, ran screaming out into the plaza, while I sipped my
coffee, looked over at a fellow Californian at the next table, and said
"What do you think, about a 5.1?"


About the phone alerts:  USGS's MyShake and other early-warning systems
are, obviously, still being worked out, but already you can tweak them a
_little_ about what not to bother you about.  I hope that gets further 
work.  Speaking for myself, because I decline to enable "location
services" on my mobile devices, MyShake inherently cannot autodetermine 
exactly what's too far from me to bother me about.

Anyway, yes, I was bothered by MyShake about that itty-bitty 4.1.  My
entire household self-protected for a bit, then realised it probably was
quite distant, and then I fired up a Web browser to check USGS and said,
"Oh, just a 4-something in the Delta."