With the adoption of the newest plumbing codes, the issue of strapping water heaters against earthquakes just went nation-wide. Mind you, the earthquake risk did not. Whitman County is still a Seismic Zone B, as is Asotin County.
The relevant code is the UPC 507.2 and was adopted by the State Building Code Council. The full text reads:
507.2 Seismic Provisions. Water heaters shall be
anchored or strapped to resist horizontal displacement
due to earthquake motion. Strappings shall be at points
within the upper one-third and lower one-third of its
vertical dimensions. At the lower point, a distance of not
less than four (4) inches (102 mm) shall be maintained
from the controls to the strapping.
This does not (I think) mandate repairs. In my reports, I will be adding the strapping as line and recommending it as an upgrade for older water heaters. For installations after July 1st, a lack of strapping will be listed as a repair item.