It took a 7.1 quake to make me ask, What happened to the Richter Scale?

It's an overcast, June gloom (in July), Monday morning as I write this.  Last Thursday was the 4th of July, and I was sitting in this same McDonald's when I felt a jolt.  Consciously, I didn't think much of it.  If you had asked me, I would have said someone must had bumped into the back of the booth I was sitting in.  But then a woman sitting nearby said, "Was that an earthquake?"  We felt a mild aftershock a couple minutes later, and decided, "yes, that was an earthquake." 

That's usually how earthquakes go here in Southern California.  You feel something, you think someone is shaking the bed, table, chair, car, whatever you're in or on.  Then you look up, see no one, and say, "Oh, that was an earthquake."  Then you turn on the TV, or these days the phone or computer, and see a news video of a woman at Cal Tech telling you how big that earthquake was, and where the epicenter was.  You figure out, roughly, how many miles away you are.  After that, maybe 10 minutes later, videos start coming in that show lights swinging, windows rattling, and some store, somewhere near the epicenter, where a whole bunch of stuff fell off the shelves.  That's what nearly all the earthquakes I've experienced have been like. 

Personally, I've always found earthquakes pretty interesting, and kind of fun, but they scare the shit out of a lot of people.  I guess it's the surprise factor, and the fact that you can't really do much, but run to a doorway, run outside, or hide under something big, halfway through one.  My whole life, we hear the number of the earthquake, the magnitude, and we always thought that it was the Richter Scale number we were hearing.  But looking into the July 4th (2019) quake, I learned that earthquakes are now measured by something called the Moment Magnitude Scale, not the Richter Scale we've all heard of, and thought was still in use.

The Richter Scale was invented in 1935 by Charles Richter, as a way of measuring large earthquakes in Southern California.  By measuring the seismic waves on a certain type of seismograph, and knowing the distance these were detected from the earthquake epicenter, Richter could use an algorithm, and put a number on the quake that could be compared to other earthquakes in a fairly accurate way.  But the Richter Scale worked best with larger earthquakes, not ones below a 5 on the scale.  Each number designation was a 10 times bigger waves than the previous number.  So a Richter Scale 6 earthquake had waves 10 times bigger than a Richter Scale 5 earthquake.  But the Richter Scale needed to know the exact location of the seismograph from the quake epicenter, it didn't work well on smaller earthquakes, and the highest number on the scale was a magnitude 7. 

As with all technology, seismographs improved over time, and became better at recording earthquake data.  In 1978, the Moment Magnitude Scale was invented by Tom Hanks (not the actor), and Hiroo Kanamori.  Their scale used the actual rock break in the earth, the length and width of the break or slip, along with the strength of the rocks that broke, to develop a better, more accurate scale, the Moment Magnitude Scale (Mw).  This scale focused on the amount of energy released at the moment of the earthquake.  Like the Former Richter Scale, the Moment Magnitude Scale has waves about 10 times bigger for each whole number of the scale.  But the Mw scale really measures the energy released, which is about 32 times more energy for each whole number of the scale.  So a Mw magnitude 6 earthquakes has seismic waves 10 times bigger than a magnitude 5, but releases 32 times more energy in that moment, than a magnitude 5.

On the evening of July 5th, I was sitting at another McDonald's, mostly because I'm currently homeless, and they have $1 Diet Cokes and wifi.  With the 6.4 quake happening the day before, earthquakes were on all of our minds.  So when I felt a weird bouncing feeling, I looked up, wondering if it was an after shock.  Another guy at McD's looked up as well, and we both asked, "Was that an earthquake?  We decided it was.  The rolling feeling, like being in a small boat as waves roll under it, faded slowly, then it came back, MUCH stronger, and it just kept going and going.  The hanging lights in that McDonald's were swinging wildly, the big windows next to me rattled, and someone pointed outside.  The big poles hanging over the nearby intersection, which held the traffic light, were visibly bouncing about a foot up and down.  The quake kept going for what felt like far more than a minute.  I actually started to get motion sickness before it ended.

The guy who noticed the quake first got on his phone, and got the magnitude before I could on my laptop, 7.1, quite a bit bigger that the day before.  It definitely lasted a lot longer, maybe 2 to 3 minutes or more of shaking.  I know from experience, 15 to 30 seconds is a long earthquake.  This one went on much longer than that. 

As I looked it up online, I found this Cal Tech earthquake map, Recent Earthquakes in California and Nevada- Index Map (link below), which I've been geeking out on since.  As I sat in that McDonald's, I kept checking the map, to see that we had like 18 earthquakes over 4.0 magnitude (Mw), in an hour.  By clicking on the big earthquake, and then updating, I saw that we didn't just have a 7.1 earthquake.  From 8:16 pm Friday evening (July 5th, 2019) to 8:25 pm, we had multiple earthquakes with magnitudes of 5.0, 7.1, 4.6, 5.0, 4.0, 4.3, and another 5.0.  So we must have felt the initial 5.0, looked up, started talking, and then the 7.1 hit and the others kept us rolling and bouncing, about 150 miles from the epicenter in Ridgecrest CA, for 2 or 3 minutes.

By clicking on one of the squares on that map, representing a single one of the many earthquakes, it brings up the most recent quake over 3.0, and then a whole list of all the quakes around it, a long list.  There have been 5,777 measurable earthquakes in that Ridgecrest area (and all of California/Nevada), starting a little while before the July 4th 6.4.  Even now, 2 1/2 days after the 7.1, there was a 3.2 quake out there an hour and a half ago, and 20 or more smaller ones after that.  The rocks, heck, the whole mountains, are moving.  A lot. 

So that's what I've learned from our pair of big SoCal earthquakes these last few days.  Here are some links on the Richter Scale, the Moment Magnitude Scale, and Cal Tech, along with links to the major earthquakes I've been through in my life. 

The Richter Scale- wikipedia
The Moment Magnitude Scale explained (or watch the more techie oriented video above)
Cal Tech's Recent Earthquakes in California and Nevada- Index Map

1983 6.9 Borah Peak earthquake- Idaho-  120 miles from epicenter

1987 5.9 Whittier Narrows Earthquake- L.A. area- 10 miles from epicenter 
1989 6.9 Loma Prieta Earthquake- San Francisco Bay Area - I wasn't there, but my sister Cheri was 10 miles from the epicenter, far closer than the freeway bridges that collapsed in Oakland.
1994 6.7 Northridge Earthquake- North of L.A. - 60 miles form epicenter
2011 5.8 Virginia Earthquake - Northwest of Richmond, VA -  175 miles from epicenter, I didn't feel this one, but many people nearby did, entire office buildings were evacuated in downtown Winston-Salem.  This earthquake was felt by more people in North America than any other modern earthquake, and it's the one that damaged the Washington Monument. 
2019 6.4  July 4th Ridgecrest Earthquake, 120 miles NE of L.A.- 150 miles from epicenter
2019 7.1 Ridgecrest Earthquakes- 120 miles NE of L.A.-  150 miles from epicenter, this cluster of earthquakes included 5,777 earquakes (so far), including quakes with magnitudes of: 5.4, 5.0, 5.0, 5.4, 5.5, and 5.4, as well as dozens of quakes in the 3.0 to 4.9 range.