Question

If the San Andreas fault moves 2 meters ( \(6.6\) feet) per big earthquake, and plate movement is \(2.5\) centimeters (0.025 meter per year, or 1 inch per year), how many years of plate motion must accumulate to produce one big earthquake? (Assume all plate motion is accommodated by movements on the San Andreas fault.) a) 4 years b) 20 years c) 80 years d) 200 years

Short answer

c) 80 years

Step-by-step solution

Understand the Given Information

We need to determine the number of years required for the plate movement to accumulate to cause a 2-meter shift in the San Andreas fault. This is known to happen in each big earthquake. The annual plate movement is given as 0.025 meters, or 2.5 centimeters.

Set Up the Equation

We need to find out how many years it will take for the total cumulative plate movement to equal 2 meters. We express this in the equation form: \[2 = 0.025 \times \text{years}\]

Solve the Equation

To solve for the number of years, divide both sides of the equation by 0.025: \[\text{years} = \frac{2}{0.025}\] Evaluating this, we get: \[\text{years} = 80\]

Compare with the Options

The calculated number of years is 80. Reviewing the options provided in the problem: - a) 4 years - b) 20 years - c) 80 years - d) 200 years The correct answer is option c) 80 years.

Key concepts

San Andreas Fault

The San Andreas Fault is one of the most famous fault lines in the world. This massive crack in the Earth's crust stretches about 1,200 kilometers through California. It's the boundary where the Pacific Plate meets the North American Plate.

The fault is a transform fault, which means it is mostly caused by horizontal slip between the plates. These horizontal movements result in some significant earthquakes. When stress builds up along the fault, it eventually gets released in the form of earthquakes. The San Andreas Fault is known for its potential to produce major seismic events.

Since it's such a well-known fault line, scientists frequently study it to understand the mechanics of earthquakes and improve prediction efforts.

Earthquake Prediction

Predicting earthquakes is a challenging science. Despite advancements in technology, it remains difficult to predict exactly when and where an earthquake will happen.

Scientists focus on monitoring fault lines, like the San Andreas Fault, to understand how stress builds up over time. They use various methods:

• Seismometers to detect ground vibrations.
• GPS to measure changes in the Earth's surface.
• Historical data to identify patterns in earthquake activity.
• Geological studies to learn more about fault structures.

While these methods provide valuable data, they mostly help in understanding long-term patterns rather than predicting specific earthquakes. Instead of exact predictions, scientists can often estimate probabilities of earthquake occurrences in certain areas over extended time frames.

Plate Movement Calculation

Calculating plate movement helps scientists understand how stress accumulates on fault lines like the San Andreas Fault.

Plate movement is typically slow, often just a few centimeters per year. However, over time, this movement can add up, leading to significant geological shifts.

Let's revisit the original problem: if the San Andreas Fault moves 2 meters in each big earthquake, and the plates shift at 2.5 centimeters per year, we need to calculate the accumulation time.

• Given: annual movement = 0.025 meters per year.
• Accumulation required for big earthquake = 2 meters.

The equation to solve is straightforward: \[2 = 0.025 \times \text{years}\]Solving this gives:\[\text{years} = \frac{2}{0.025} = 80\]This tells us it takes about 80 years for the plate movements to build enough stress to potentially cause a major earthquake along the fault.