A direct line to earth's tensions
The hot springs of Alhama de Granada emerge along a major geological fracture, the Alhama de Murcia Fault. This structure is a nearly 100-kilometer-long strike-slip fault system that is a zone of weakness in the Earth's crust. It forms part of the larger Betic Cordillera, a mountain range created by the ongoing collision between the African and Eurasian tectonic plates. This immense pressure creates deep fissures that allow groundwater to descend, heat up due to the geothermal gradient, and then ascend back to the surface.
The resulting thermal waters emerge at a constant temperature between 42 and 47 degrees Celsius. They are minerals, classified as sulfate-calcium-magnesium bicarbonate waters, which have been used for their therapeutic properties since at least the Roman era. The town's name itself, "Alhama," derives from the Arabic "Al-Hammah," meaning "the bath," shows the springs' long history. Inside the modern spa, a 12th-century Almohad bathhouse, built upon 1st-century Roman foundations, remains.
Reading the gas signals
This direct plumbing to the deep subsurface shows the stresses building within the fault. Scientists monitor the gases dissolved in the thermal waters, particularly radon-222. Radon is a naturally occurring radioactive gas produced by the decay of uranium present in the rocks. Under normal conditions, much of this gas remains trapped. However, as tectonic stress accumulates before an earthquake, it is hypothesized that micro-cracks form and expand in the bedrock. These new pathways allow trapped radon to escape and dissolve into the groundwater that feeds the springs.
Studies have shown that radon concentrations in the water can increase significantly in the weeks preceding a seismic event. This phenomenon makes the springs a natural laboratory for studying earthquake precursors. Although not yet a definitive forecasting tool, continuous monitoring of radon flux, alongside other geochemical signals like changes in carbon dioxide and hydrogen, is a field of research for developing early warning systems for seismic activity in the region. Researchers correlate anomalies in the gas data with seismic events, noting that precursor times can range from a few days to several weeks.