  We present the design of a cross-layer protocol to maintain connectivity in
an earthquake monitoring and early warning sensor network in the absence of
communications infrastructure. Such systems, by design, warn of events that
severely damage or destroy communications infrastructure. However, the data
they provide is of critical importance to emergency and rescue decision making
in the immediate aftermath of such events, as is continued early warning of
aftershocks, tsunamis, or other subsequent dangers. Utilizing a beyond
line-of-sight (BLOS) HF physical layer, we propose an adaptable cross-layer
network design that meets these specialized requirements. We are able to
provide ultra high connectivity (UHC) early warning on strict time deadlines
under worst-case channel conditions along with providing sufficient capacity
for continued seismic data collection from a 1000 sensor network.
