New research shows magma is accumulating beneath a fault slip near the capital of El Salvador. The fault slip is located beneath Ilopango caldera.

The latest findings, detailed in the journal Nature Communications, suggest San Salvador is at risk of future rumbles and ruptures.

Researchers from Bristol University believe Ilopango offers geologists a chance to better understand the links between earthquakes and volcanoes.

"Most earthquakes take place along the edges of tectonic plates, where many volcanoes are also located," Joachim Gottsmann, project leader and study co-author, said in a news release.

Ilopango is one of several calderas in the Central American Volcanic Arc -- a string of volcanoes stretching from Guatemala to Panama -- situated within a system of tectonic fault zones.

"There is therefore a link between the breaking of rocks, which causes faults and earthquakes and the movement of magma from depth to the surface, to feed a volcanic eruption," Gottsmann said. "The link between large tectonic fault zones and volcanism is, however, not very well understood."

Gottsmann and his colleagues at Bristol recently analyzed the relationship between the density distribution beneath the Ilopango caldera and the location of fault slips.

Calderas like Ilopango are formed when magma chambers are emptied during a large eruption or series of eruptions. Ilopango was formed by a series of five major eruptions over the past 80,000 years. Previous studies have suggested fault structures influence caldera-forming eruptions and the nature of the caldera collapse.

The latest analysis suggests current tectonic stresses are encouraging the accumulation of gas-rich magma beneath Ilopango, a phenomenon that could fuel the volcano's next eruption.

"This fault-controlled magma accumulation and movement limits potential vent locations for future eruptions at the caldera in its central, western and northern part -- an area that now forms part of the metropolitan area of San Salvador, which is home to 2 million people," Gottsmann said. "As a consequence, there is a significant level of risk to San Salvador from future eruptions of Ilopango."