What physical property, besides chemical distinction, characterizes the LLSVPs when measured by seismic wave travel time variations?

They possess physical properties vastly different from the surrounding rock

The identification of the anomalies relies on the way seismic waves interact with them during travel. A wave passing through the LLSVPs experiences significant deviations in travel time compared to waves passing through the normal lower mantle. This variance indicates that the physical properties of the anomalies—which include density and seismic velocity—are substantially different from the ambient material. The text uses the analogy of ripples traveling across still water versus thick mud to illustrate this impedance contrast. The fact that these features register as significant deviations means they are physically distinct provinces whose internal structure and composition deviate strongly from the churning rock that characterizes the rest of the mantle.