National Richter Scale Day Calendar Add to Calendar Add to Timely Calendar Add to Google Add to Outlook Add to Apple Calendar Add to other calendar Export to XML When: April 26, 2021 all-day Repeats 2021-04-26T00:00:00-05:00 2021-04-27T00:00:00-05:00 Where: National Richter Scale Day United States NATIONAL RICHTER SCALE DAY National Richter Scale Day is observed annually on April 26th. This day honors the birth of the Richter Scale inventor, Charles F. Richter (April 26, 1900 – September 30, 1985).