Answer by Matthew Sutton:
Concrete is more problematic than steel due to its brittle nature. If the reinforcing is done correctly, particularly at the connections, (all beam/slab design per ACI should be OK), and around the shear walls they should be safe. I say ‘should’ because the current ACI and CBC code provisions are untested. The most recent seismic design provisions in CA were developed largely in response to Northridge. Ongoing research into structural failures in Japan and New Zealand will certainly yield new insights and new code recommendations, some of which may eventually get adopted…but these countries aren’t using the ACI code so it’s a bit of an apples to oranges comparison.
Steel structures are generally less susceptible to structural failure due to the ductile nature of steel and they’re ability to dissipate energy. However weak links like poorly designed braced/moment frames, connections, or soft story behavior with slender columns, can all compromise a steel building. Even steel buildings that survive an earthquake may be well beyond repair due to excessive damage or deflections.
Vulnerability needs to be defined with some precision–vulnerable to damage, less resilient, more of a threat to the life-safety of the occupants?