San Diego Geologic History and Natural Hazards Summary Research Paper

San Diego Geologic History and Natural Hazards Summary - Research Paper Example The contact experienced between these geologic regions is irregular and this reflects the ancient area topography before being buried by the thick sequence of Tertiary and Cretaceous sedimentary rocks that was deposited by ancient seas and ancient rivers over the last 75 million years (Abbott, P, 23) Both these rocks with their existing biological record such as the fossils, document the biological and geological evolution of this western North America part. It is recorded that at a certain point in time, there was an ancient oceanic crustal plate consumption that created volcanic islands archipelago and also this same plate subduction generated massive magma volumes which in the later stage congealed in the crust that resulted to plutonic rock. It is also observed that local rocks record an early period when erosion unroofed and tectonic forces uplifted the plutonic rocks that were deeply buried forming a rugged and steep mountainous coastline. This is similar to the one present today along the west coast of South America. Also recorded are periods of subtropical climates and higher rainfall that supported coastal rain forests with exotic floras and faunas; relentless erosion, drowned coastlines periods and great rivers; periods of extreme renewed and aridity volcanism; widespread crustal shear and faulting periods and the new seaways formation (Bergen et al, 34). The above are just some of the stories of geology preserved in the San Diego County. Deciphering the biological and geological record is a process that is ongoing and every year brings new insights and new discoveries. Geographical regions of San Diego affected by Natural Hazards The processes of natural geology which represent a hazard to health, property or life are taken to be geologic hazards. Natural geologic hazards which affect property and people in San Diego County include earthquakes that can result to ground shaking, liquefaction and surface fault rupture, expansive weathering soils, and phenomena mass wasting such as rockfalls and landslides (Bray and Kelson,5).The hazard of surface rupture has been identified as Alquist-Priolo Earthquake Fault Zones (AP Zones). Two major AP Zones extend to southeast from northwest across the northeast half of the County, the San Jacinto and Elsinore fault zones; present the highest fault-rupture threat in the unincorporated San Diego County part (Anderson et al,13).Liquefaction primarily occurs in loose, saturated and fine to medium-grained soils in places where the groundwater table is basically at most 50-feet below the surface. There may be a potent ial for liquefaction within the County in areas with loose sandy soils together with a shallow groundwater table, that are typically located in floodplains and alluvial river basins/ valleys. Previous landslides together with landslide-prone sedimentary formations are located in western unincorporated County portions( Bowman,21). However, it is known that landslides can as well take place in the granitic terrain in the eastern County area, despite the prevalence is so minimal (URS, 2004). Most of the landslides that are significant have happened along coastal bluffs and other areas within incorporated County parts (URS, 2004). Existing landslides reactivations can be triggered by situations that include irrigation or heavy rainfall, seismic shaking or grading. Particular clay soils types normally shrink when dried