New Back-Office Exodus? Mergers Seen Spurring Flight from Biggest Cities The recent spate of bank mergers has observers predicting a renewed migration of back-office operations away from the nation's largest cities. Enticed by the promise of dramatic reductions in overhead and operating costs, Citicorp, CoreStates Financial Corp., and Chase Manhattan Corp. in past years have set up processing operations far from home, in Nevada, South Dakota, and Delaware. The migration from large cities slowed substantially this year. These days, few banks can spare the capital necessary to start up a new operations center. But the back-office consolidations that follow large bank mergers usually require back-office construction and juggling of personnel. For this reason, many observers said, recent merger activity will give rise to a new wave of interest in moving operations to the remote areas.