Week 6 - Geological Interpretations, San Bernardino County, CA

San Bernardino County, CA fault zones
Illustration credit:  California Division of Mines and Geology

San Bernardino County, CA is an area where multiple earthquake fault lines are present.  Within this area the San Andreas, San Jacinto and Loma Linda - Glen Helen Faults are perpendicular in part to the Cucamonga Fault.  These all generate substantial concerns for the populace of this region.  As manufacturers seek more economically sustainable alternatives to neighboring heavily populated areas like Los Angeles, the San Bernardino region offers a viable option for relocation.  However, with increased manufacturing comes urban growth.  Research and planning on the part of geological survey teams tasked with highlighting safety concerns brings several questions to the forefront (ftp://ftp.consrv.ca.gov/pub/dmg/pubs/sr/SR_113/SR_113.pdf).  

   1.  Has the amplitude of signals measuring magnetic cores in the ground changed recently in the rock of areas targeted for future industrial, commercial and residential building?  This could signal plate movement in fault lines associated with the area of concern.  Plate movement could bring with it changes in the alluvial composition of soil through shifting of softer, sandy soils into what was previously firmer bedrock.  A change in soil or mineral composition could make an area not suitable to build on.

   2.    What are current coring samples showing in the way of moisture in the soil and rock    composition?  This will help determine how deep the water table is in proposed construction sites.  Too shallow of a water table introduces problems with liquefaction when heavy rainfall and flooding occur.  In this situation the soil becomes quickly saturated and unstable making mudslides a concern.  Rainfall is not the only cause of liquefaction.  Municipal water companies will often have water routed in from other sources to augment their native supply.  If this purchased water is not managed properly, excess runoff from underground storage will also produce liquefaction problems.  Lastly, residential, industrial and commercial consumers can affect the liquefaction issue by watering lawns, washing vehicles and other forms of recreational and industrial applications that discharge water.

    3.    Any part of urban growth must factor in the consumption of water as previously alluded to.  If water is not going to be brought from another source, will the native aquifers be tapped into to any large extent?  And will there be any removal of oil in the area proposed for growth?  These two factors bring into play another concern in the way of subsidence.  Removing large amounts of fluid from underground reservoirs changes the hydraulic pressure pushing against rock and soil formations making them weaker and more susceptible to caving in.  Entire buildings have been known to fall into sinkholes caused by removing too much fluid from underground too quickly.