Discussion

Examples from previous section on Modern and Ancient Perspectives make it apparent that damage to hydrological resources due to seismic activity is a clear and present danger. For example, 37% of the United States water consumption from public sources is based on groundwater (Hutson et al., 2005). Fresh ground-water withdrawals in the United States increased by 14% between 1985 and 2000, and an estimated 242 million people nationwide, or about 81% of the US population, depend on water from public suppliers. These figures indicate that use of groundwater for the national public water supply is significant and that earthquake hazards on groundwater sources could have high social and economic impacts in various geographic regions throughout the US. Yet, the effects of earthquakes are relatively undocumented both in the ancient and modern world.

Regarding earthquake hazards on well infrastructure, the proportion of locations affected and associated economic and social consequences remain unknown. A body of research that quantifies the hydrological impact of earthquake hazards has emerged; however, there is still no systematic research on social and economic consequences of these hazards and no synthesis to evaluate risk levels. Moreover, there are no governmental committees or units that can be assigned the task of assessing this specific hazard because of the interdisciplinary nature of factors contributing to the problem. Furthermore, there is a lack of data regarding the issue of recurrent recharge after the loss of water. This would be an extremely important piece of information for both modern and ancient perspectives as it would allow one to examine: (1) Whether or not an aquifer can maintain the same recharge as in the past; (2) What the recurrence interval for the aquifer recharge (e. g., years, centuries) is?

Another area worth investigating is the extent of the effects of an earthquake on water supply are. For instance, what are critical earthquake parameters, such as magnitude and proximity to the earthquake epicenter, that represent maximum risk for wells? This information would be helpful in determining the location of wells at risk and estimating spatial extent of the potential damage caused by an earthquake. For example, it has been argued that in Crete earthquake damage is often localized and thus would not have accounted for damage throughout the island in the LM IB period (Soles, 1999). However, this refers to the damage sustained by the structures above the ground and not to water resources that are spread and located within different topographic and geomorphological units that can have different levels of resilience to the seismic wave effect. The only known studies related to this area of investigation were done first by Dobrovolsky et al. (1979) and later by Montgomery and Manga (2003) who related changes in stream and groundwater flow to earthquake magnitude and proximity. The study conducted by Montgomery and Manga (2003) showed that “the distance to which earthquake-induced changes in water levels in wells have been reported increases systematically with earthquake magnitude”. While this is an important conclusion, it only slightly advances the quantitative identification of the earthquake impact on water supply.

Geologic evidence and factors that contribute to the understanding of earthquake effects on groundwater supply come from modern studies alone. The best documented case is the Pymatuning earthquake. It provided geological and geomorphological criteria for understanding the mechanism of groundwater effects caused by the earthquake activity. While the Pymatuning model is the only case that has a comprehensive description and documentation (in addition to the Matsushira earthquake case that is less documented, but at least offers a geographic map of well locations), geologic factors described in Fleeger et al. (1999) provide a basis for generalization of geomorphologic and structural geological factors applicable to interpretation of both modern and ancient cases.

There is a definite need for a multidisciplinary study which will incorporate geological, hydrogeological, social, and economic factors in the existing known cases of well water disruption due to earthquake activity. Efforts must be undertaken to ensure complete reporting on changes in well water levels with seismic events. This practice will help scientific community evaluate risk factors, preparedness measures and mitigation strategies, and develop requirements and protocols for the assessment of the impact of earthquake hazards on well infrastructure. We need to gain a more complete understanding of the social and economic ramifications of hydrological damage caused by earthquakes in our own time in order to obtain a clearer picture of similar events in ancient times.