Question

1. practice: causes of earthquakes

question 1
how is the timing of seismic waves in an earthquake determined?
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question 2
why can seismic waves be used to determine structures and materials within the earth?
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question 3
briefly discuss how strain in a fault can be determined and used to produce an earthquake forecast.

Explanation:

Question 1:

Seismic waves' timing is determined using seismographs. These instruments record the arrival times of different types of seismic waves (P - waves, S - waves) at various seismometer stations. The time - difference between the arrival of P - waves (faster) and S - waves (slower) at a given station can be used to estimate the distance to the earthquake's epicenter.

Question 2:

Seismic waves can be used to determine structures and materials within the earth because different materials have different physical properties (density, elasticity). These properties affect the speed and direction of seismic waves as they travel through the earth. For example, P - waves can travel through solids and liquids, while S - waves can only travel through solids, which helps in identifying the composition and structure of the earth's layers.

Question 3:

Strain in a fault can be determined through methods like GPS measurements to detect ground deformation, and by studying historical seismic activity. When strain accumulates in a fault beyond a certain point, an earthquake is likely to occur. By monitoring the rate of strain accumulation and understanding the historical recurrence intervals of earthquakes in the area, scientists can make probabilistic earthquake forecasts.

Answer:

Question 1:

Seismic waves' timing is determined by seismographs recording the arrival times of different wave types at seismometer stations and using the time - differences between P - and S - wave arrivals to estimate distance to the epicenter.

Question 2:

Seismic waves can be used because different materials within the earth have varying physical properties that affect wave speed and direction, and the behavior of P - and S - waves helps identify earth's layer composition and structure.

Question 3:

Strain in a fault can be determined via GPS for ground deformation and historical seismic study. Monitoring strain accumulation and historical recurrence intervals can be used for earthquake forecasts.