Note that it is important to know what elevation corresponds to for each topography dataset you might use (i.e. the vertical datum) Global ETOPO1 bathymetry is relative to MSL (Mean Sea Level), while tsunami inundation relief is often relative to MHW (Mean High Water). These can often be combined since the difference is small relative to the resolution of the global bathymetry and the result assumed to be relative to MHW. This is important if comparing to tide gauge observation or when modeling inundation.
An earthquake source is typically specified by giving the slip along the fault on a set of fault planes or on subfaults making up a single plane. This data must then be converted into seafloor deformation to create the dtopo file needed for GeoClaw (see Topography displacement files). This conversion is often done using the Okada model as described at Earthquake sources: Fault slip and the Okada model.
Tide gauge data is often recorded relative to MLLW (Mean Lower-Low Water), so be sure to check the vertical datum.
For example, if you go to a station page such as Hilo Bay, you will see a Datums link on the left menu that gives the difference between MLLW and other water levels such as MHW, which might be the reference level for the bathymetry. (Be sure to switch from feet to meters!) Sometimes you can also select the Datum to use when retrieving data.