EMB ERJ 170/175 ER/LR
Air Traffic Control Fully Certified
Communication Breakdown; Time Pressure
Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance
Human Factors; Procedure
Aircraft X was descended in the downwind to 090. As the aircraft was approaching 090; I descended the aircraft to 085 and turned 5-degrees left (they were going to Runway 34R not the west runway). The aircraft read the instruction back appropriately. Shortly later I based the aircraft as they were showing 085. The aircraft read back the instruction and I noticed the tag at 083. I immediately keyed up and verified they were level 085; they said we are leveling right now at 080. They were already in the base turn and turning away from the higher terrain; so I did not issue a low altitude alert or climb and told them to maintain 080. I reviewed the tape and the aircraft did read back 085. They were still in the 085 MVA at 080. With a proper read-back there is nothing to do to stop this from happening. Maybe 500 ft. altitudes are confusing to pilots? I've never had an aircraft bust an altitude with this before; so I don't think I would change anything.
S56 Tracon Controller reported E175 descended below assigned altitude resulting in an MVA violation.