Yesterday's 4.4 magnitude earthquake in the Los Angeles area and a 5.0 magnitude earthquake in Iquique, Chile, prompted today's topic. I thought I would shake things up a bit after the "Shamrock Shake" and the quake in Chile that prompted the evacuation of 100,000 people.
I am curious about whether you realize the U.S. Geological Survey, as well as most countries except Russia, no longer uses the Richter Scale as a measure of magnitude. The Moment Magnitude Scale, abbreviated MMS or Mw was developed in 1979 and more accurately reflects differences in energy released, particularly those above 7.0 on the old Richter Scale. Yet, the Richter Scale is more accurate for quakes of magnitude 3.5 and less.
Both the Richter Scale and the Moment Magnitude Scale are calibrated similarly for medium sized quakes (3.5 - 7.0). The numbers for quakes higher than 7.0 are generally revised upward. The March 27, 1964, Alaskan earthquake is now a 9.2 (It was 8.4 on the Richter Scale.) Note the 33 foot scarp with dessicated, white marine organisms along the newly created flat portion:
This 4 minute video about the Alaska quake was just released by the USGS to honor the big L anniversary:
50Th Anniversary of 1964 Alaska Quake: USGS Video
The May 22, 1960, Chilean earthquake, the largest seismic event recorded, has been recalibrated to a 9.5.
Both scales take into account a logarithmic scale such that the increase from one step to the next is a 32 fold increase in energy and the increase from two steps apart is 1000 fold for those medium earthquakes. The MMS moves off much higher for quakes in the upper ranges. (See video at the end of this blog for more detail).
Dr. Waverly Person, (yes, that's his real name) former Director of the USGS Earthquake Information Center here in CO, was responsible for converting quakes to the new scale, the one that hardly anyone knows. Just like our petrography friend, Dr. Nicol, that first name of Richter sticks. All the reports I read today included the Richter Scale.
If you are interested in a spaghetti-based video explaining the differences between the scales, watch here:
The moral of this tale: get in there early in the name game!
And be safe in a shake!
Looking forward to p and s waves coming from you this week.