Hydrologic Precursors

Predicting earthquakes is a long-desired goal. The main challenge is to identify precursory signals that reliably predict the impending earthquake. Since hydrological and hydrogeochemical properties and processes can be very sensitive to minute strains, the hope is that measurements from hydrological systems might record precursory rock deformation that would otherwise be undetectable. Of the many hundreds of studies, we review a subset to illustrate how signals can be challenging to interpret and highlight questions raised by observations—examples come from China, Japan, Taiwan, India, the USA, Russia, France, Italy and Iceland. All are retrospective studies. Some signals seem to have no other explanation than being precursory, however, rarely is enough data available to undertake a thorough analysis. Some hydrological precursors might be recording deformation events that are slower than traditional earthquakes (and hence usually harder to detect). Long times series of data are critical for both identifying putative precursors and assessing their origin and reliability.

CHARAKTERISTIKA ANOMÁLNÍHO SKAPU V PUNKEVNÍCH JESKYNÍCH (MORAVSKÝ KRAS)

Cave speleothems grow from supersaturated dripwaters and store information about various karst processes along the water flow path. Anomalous non-saturated waters may occur if (1) rainfall water passes very rapidly through karst profile or if (2) two saturated waters of different compositions are mixed. The low mineralization close to saturation could be reached also as (3) result of calcite precipitating prior the water enters the cave. The hydrogeochemistry of four dripwaters in the Punkva Caves (Moravian Karst) was systematically studied for anomalous properties during one-year period. The drips are situated in a passage behind Přední Dóm Chamber (CP1 and CP2, 24 samples each), in Tunnel Corridor (TC1, 24 samples), and in Zadní Dóm Chamber (ZD1, 6 samples). The dripwaters CP1, CP2, and ZD1 show various flow regimes but very similar hydrogeochemical properties: electric conductivity (EC = 550–630 μS/cm), saturation (SIcalcite = 0.8–1.2), and Mg/Ca ratio (1000*(Mg/Ca) = 15–20). In contrast, the dripwater TC1 shows stable drip rate and EC = 275–350 μS/cm, SI = -0.1 to 0.3, and almost thrice as high Mg/Ca ratios as other drips. High and stable discharge of the drip TC1, combined with low EC, SI close to zero, and high Mg/Ca ratio indicate that a prior precipitation of calcite is responsible for the anomalous composition of the dripwater. The slightly negative SI values that were occasionally observed indicate that further minor processes probably participate on the water formation.