Earthquakes near Kilauea's deep magma conduit
U.S. Geological Survey
Earthquakes provide the best evidence for the location of Kilauea's magma conduit. Long period (LP) earthquakes are caused by magma flow and show conduit location most clearly. LP earthquakes form a broad cluster 30 km south of Kilauea at 60 to 30 km depth, and also reveal vertical conduits directly below Kilauea and Mauna Loa calderas in the 30-50 km depth range. This broad cluster is interpreted as the center of the Hawaiian hot spot. A cluster of brittle failure (BF; short period) earthquakes, with larger magnitudes up to 5, is below Kilauea from about 25-35 km depth. The BF earthquakes show lateral faulting on sub-horizontal fault planes, but are related to the magma conduits which pass through the fault planes where the faults are most seismically active. Causes of deep Hawaiian earthquakes are a combination of:
There was discussion of what the earthquake cloud could say about interconnectedness of magma reservoirs and conduits at depth. The earthquake locations suggested that Mauna Loa and Kilauea could both fed by the same magma reservoir, but the dissimilarity of geochemistry of those magmas precludes this. It was pointed out that the LP earthquakes may indicate where magma or other fluids are moving, but the BF earthquakes only indicate where rock is breaking or pre-existing faults are slipping. The earthquake distribution, on the other hand, cannot rule out that processes such as magma flow may be ocurring in aseismic parts of the area. Since magma chambers are expected to be aseismic, the pattern of earthquake locations can only reveal volumes where magma chambers are unlikely to lie, and cannot conclusively indicate where they are.