Schugel, 26, has been a starter throughout his Minor League career with the Angels and D-backs, posting a 32-34 record and 4.04 ERA in 139 games, including 109 starts, over six seasons. He was designated for assignment last week when the D-backs needed to open a 40-man roster spot after signing free-agent right-hander Zack Greinke.
Schugel split last season as a starter between Double-A Mobile and Triple-A Reno, then was promoted to the D-backs on Aug. 30 and had a 5.00 ERA in nine innings over five relief appearances.
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Schugel was drafted by the Angels in the 25th round of the 2010 Draft as an infielder out of Central Arizona College and didn't convert to pitching until starting his pro career. His father is a longtime Major League scout who is currently a special assistant in the Reds organization.
Olson began last season on Seattle's 25-man roster, going 1-1 with a 5.40 ERA in 11 relief outings before being placed on the 15-day disabled list with a bruised knee. He closed out the season in Triple-A Tacoma, posting a 3-5 record and 4.47 ERA in 25 games, including six starts.
The 26-year-old was selected by Seattle in the seventh round of the 2013 Draft out of Gonzaga and is 17-17 with a 3.86 ERA in 70 Minor League games, including 41 starts. The Mariners now have 10 days to trade, release or outright Olson to the Minors.
Schugel becomes the 18th new player on Seattle's 40-man roster since general manager Jerry Dipoto took over near the end of last season.
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB, read his Mariners Musings blog, and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.