Mathematical Applications: Assessing Risk and Subsidence

Calculating risk using the standard hazard equation and evaluating rates of land subsidence.

Example

Problem 1: Evaluating Subsidence Rates

A city built on thick clay deposits relies entirely on groundwater pumping. In 1990, the benchmark elevation of the city center was 15.500 m15.500 \text{ m} above mean sea level. By 2020, due to excessive groundwater extraction and subsequent clay consolidation, the same benchmark was surveyed at 13.100 m13.100 \text{ m}. Calculate the average annual rate of subsidence and project the elevation in the year 2050 if this rate remains constant.

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Example

Problem 2: Calculating Basic Risk

A regional planning commission is evaluating the risk of a major landslide affecting a newly constructed highway. Geologists estimate the annual probability of a major landslide (the Hazard) at this specific location is 0.050.05 (5%5\% chance per year). The highway itself cost 50 million50 \text{ million} to build, but a major landslide would completely destroy a 2 km2 \text{ km} section, causing an estimated 15 million15 \text{ million} in direct repair costs and economic losses (the Exposure). Because the highway is the only route to a major port, its destruction would cause severe disruption; thus, its Vulnerability factor is rated at 0.80.8 (80%80\% of the exposed value would be effectively lost). Calculate the annual Risk in dollars.

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Example

Problem 3: Comparative Risk Analysis

A city must choose between allocating funds to mitigate one of two different geological hazards affecting two separate neighborhoods.
Neighborhood A (Flood Hazard):
  • Annual Probability (HH) = 0.100.10 (10%10\%)
  • Total Property Value (EE) = 20 million20 \text{ million}
  • Vulnerability (VV) = 0.20.2 (minor damage, mostly cleanup and drywall replacement)
Neighborhood B (Rockfall Hazard):
  • Annual Probability (HH) = 0.020.02 (2%2\%)
  • Total Property Value (EE) = 5 million5 \text{ million}
  • Vulnerability (VV) = 0.90.9 (catastrophic structural destruction, lethal hazard)
Calculate the annual risk for both neighborhoods to determine which presents the higher economic priority.

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Case Studies: Geological Hazards

Understanding the devastating impacts of complex geological hazards on infrastructure.

Example

Case Study 1: Volcanic Hazards - Lahars and Bridge Design

A major international highway bridge is being constructed across a wide, shallow river valley whose headwaters originate on the heavily glaciated slopes of an active stratovolcano located 40 km40 \text{ km} upstream.

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Example

Case Study 2: Problem Soils - Differential Settlement on Expansive Clays

A large, sprawling residential subdivision consisting of hundreds of single-family homes is built upon a flat, arid plain composed almost entirely of thick, expansive smectite clay deposits (montmorillonite). The region experiences severe, distinct wet and dry seasons.

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