More quakes rock central U.S. and Alaska
Posted on Jun 12, 2019
A magnitude 5.0 earthquake struck early Friday in the Midwest, shaking the ground for about five seconds in Tulsa, Oklahoma, Wichita, Kansas, and other nearby cities, reports said.
Moments later, a magnitude 5.6 quake reportedly shook Adak, Alaska, in the Bering Sea, nearly 4,000 miles away.
What’s causing this uptick in seismic activity?
According the the United States Geological Society (USGS ), a temporary increase or decrease in seismicity is part of the normal fluctuation of earthquake rates.
Between 1973–2008, there was an average of 25 earthquakes of magnitude three and larger in the central and eastern part of the country. This rate ballooned to over 600 M3+ earthquakes in 2014 and over 1000 in 2015, but has decreased some in recent years.
However, the notable fact is that recent quakes are often affecting areas previously thought “safe.”
You may remember the 4.0 magnitude earthquake that recently hit the Cleveland, Ohio area in June 2019.
Because of this shift, the USGS is reevaluating the hazard due to induced earthquakes and has reevaluated seismic design categories and the building and rack requirements for many areas of the country.
How do changing seismic design categories affect rack requirements?
With a better understanding of structural performance during an earthquake event, standards will continue to evolve, placing more demand on the rack design.
Per Steel King’s in-house industry expert Arlin Keck PE, “Old habits are hard to break. Unfortunately, that also pertains to old perceptions. Many of us remember when the only time that seismic design was considered was for installations going into California (and possibly the St. Louis – Memphis corridor). As the recent earthquake in Lake Erie illustrated, that is no longer the case. When purchasing new storage racks, it behooves the end user to choose a rack manufacturer (that) is an R-Mark certified member of the Rack Manufacturers Institute, to design your racking system to assure that the structure is seismic-compliant.”
The Rack Manufacturers Institute (RMI) Standard is the recognized U.S. specification for the design, testing, and utilization of industrial steel storage racks. Responsible rack users will want to demonstrate that their racks meet this recognized standard for seismic design. RMI created the R-Mark Certification Program as a way for storage rack users and customers to clearly identify those rack manufacturers whose components and design are in accordance with the RMI Specifications. Steel King® is one of 22 rack manufactures that holds an active R-Mark License.
Another consideration is that one of the continuing trends within warehousing includes automation – in the form of both pick modules and automated storage and retrieval systems. Both systems raise the stakes of a potential rack collapse – in terms of expensive equipment and the lives of people working within the structure.
Rack systems should be designed, manufactured, installed and used in accordance with seismic requirements for maximum safety.