Problems / Raised type
Age
Homes built before 1950 have serious flaws in the foundation. These include poor materials in the the concrete, no reinforcement (rebar), no connection between sill plate and foundation (foundation bolts), and footings (6" or less.).
Wear
Due to the poor materials and construction techniques, older homes are more vulnerable to the effects of water, weather, and aging
Settlement
Many areas of San Diego have houses built on clay soil. Clay soil shifts seasonally as the ground becomes wetter in the winter and drier in the summer. This results in sloping floors, doors that don't close properly, distress to paint and plaster.
earthquake protection
With no proper connection between the house and the foundation, a strong earthquake can move the house off the foundation, causing structural damage. Crippled walls that are not properly braced can collapse as the vertical wood (studs) fall as a unit.

Problems / Slab type
Minor cracks
Small cracks with no differential can be caused by shrinkage of the concrete after pouring, minor earthquakes and poor soil conditions.
Major cracks
Large cracks are typically caused by improper fill soils, expansive soil, and lack of reinforcement.
Settlement
Many areas in San Diego have clay soils. Moisture can seep under footings, causing lifting and settlement of the perimeter. Furthermore, uncompacted fill soils can settle over time as moisture causes the soil to compact.
Doming
Dated construction techniques or drainage problems can cause the perimeter to sink, and can cause clay soils to expand, lifting concrete slabs.