Doors and Windows - Attic door widening potentially gone wrong

Well, we recently made an offer on a house in California. During the home inspection, one of the things that came up was that the sellers at some point had increased the size of a door going in to an attic. The door was there as part of the original construction. Now, the problem is that this door was cut in to a shear wall. In widening the door, one of the double studs in the wall was cut. This is on the side away from the hinges, where the door knob is. My question is that,
1. Being in an earthquake zone, has this significantly weakened the structure
2. Is it possible that the contractor who did the widening, did not put in a stud on the door-knob side to support the door frame.

I should also mention that the entire door frame sits about a foot above the floor level.

Any advice is welcome. Please let me know

Welcome to the forums! Speaking generally, if the door was there as part of the original construction, it had to pass a stringent inspection in California. If it was properly headered and supported on both sides with jacks and kings, there should be no problem. It is not likely the contractor didn't put a stud on the latch side. There would be no time savings and the door would have been more difficult to install without it. As far as earthquake stuff, you probably should consult a structural engineer.

Thank you, Chandler, for the response and the welcome note. I went to the house with a ultrasonic stud finder and checked. The door as expected, has a stud supporting it on the latch side. Also, because the door is so close to a corner, there is one double stud and the relocated stud quite close to each other. The handyman who accompanied me also approved of the job. I am reasonably satisfied that moving the stud 6 inches did not weaken the structure by a worrisome amount.