Jana Jackson Exercise 7.8
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Central Piedmont Community College *
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101
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Geology
Date
Apr 3, 2024
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docx
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2
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Jana Jackson
Exercise 7.8 (a) Briefly describe how the water table relates to past episodes and locations of liquefaction in San Francisco. Why does it seem important to study the water table when considering the possibility of liquefaction? -
The water table relates to past episodes and locations of liquefaction in San Francisco being that it shows the boundary that is between the saturated and unsaturated zone that’s
underground. Groundwater fills the spaces between sediments and inside of rock formations below the water table. Because a dip in the water table might cause voids to appear at the surface, this emphasizes how important it is to look at the water table when evaluating the likelihood of liquefaction. It’s important to study the water table when considering the possibility of liquefaction because it helps to indicate soil saturation, groundwater influence and can help to determine overall mitigation strategies. (b) Compare the locations of the 1989 liquefaction events with the water table elevations in the previous diagram. Does the relationship between liquefaction and water table elevation you discovered in question (a) also apply to all of these areas? If not, suggest possible explanations for the difference.
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In all of these cases, the association I found in question between liquefaction and water table elevation is true. As the water table contour levels in the figure are low, indicating shallow water tables, the 1989 liquefaction spots are all along the seashore.
(c) Now look at the locations of the 1989 liquefaction events that occurred in places not affected by the 1906 earthquake. (i) Are they randomly distributed throughout the region or restricted to specific locations? Explain. -
The locations of the 1989 liquefaction events that occurred in places that were not affected by the 1906 earthquake are all located along the eastern shoreline of San Francisco. (ii) Are they located in areas of varied susceptibility to liquefaction or in areas with the same level of susceptibility? Explain. -
All the locations fall within the same level of susceptibility, which is designated as 'Very high susceptibility' on the map. This may be because of these areas being considered during the assessment of hazard susceptibility, or it could indicate a common underlying vulnerability that makes this zone particularly prone to risk.
(iii) Compare the 1989 liquefaction sites with the map of shoreline changes on the right below. Why did the 1989 earthquake affect these areas, but not the 1906 earthquake? -
A number of the locations impacted in 1989 were underwater when the shoreline showed noticeable changes in 1906. Since 1906, these areas have been filled in with waste,
making them vulnerable to impact in 1989. Thus, the regions that were spared from the disaster in 1906 saw its consequences in 1989.
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