Yes, a large earthquake on the West Coast would be devastating to the economy because natural disasters usually impacts financial markets and the earthquake would destabilize everyday life in the West Coast. A large earthquake in the West Coast would definitely have disastrous effects to the economy not only because it would disrupt everyday life but also because the government would have to shell out billions of dollars in relief funds.
Natural disasters are exactly that, disasters. They create a disaster both to land, homes, and the economy. If businesses are unable to operate because of an earthquake then everyone suffers for it. Business owners cannot provide a service, consumers cannot purchase that service and therefore business owners cannot continue to pay their employees or create supply. It would be a cycle of disaster.
California alone is one of the largest economies in the World. Las Angeles and San Diego are major global cities with huge contributions to our economy. A devastating earthquake would cause substantial economic hardship to our economy. It would take years for us to recover from such a disaster; potentially creating a second great depression.
An earthquake that devastated our west coast would be devastating to our economy. First, there are several major points of import for goods from Asia located up and down the west coast. Second, there is a large base of companies in the computer and technology industry scattered from California all the way to Washington state. It wouldn't just devastate our economy, it would set our technological developments back on their heels and put all advances in those fields on hold indefinitely.