David Shelly, a seismologist at USGS and helped write the study, in a statement. "And they tell us a lot of things about that deep part of the fault that we had no idea about before."

　　"It's almost like having a lot of little creep meters embedded in the fault,"Shelly said. "We can use these low-frequency earthquakes as measurements of, at least in a relative sense, how much slip is happening at each little spot on the deep part of the fault where we see these events. When we don't see them, we don't know what's happening; we don't know whether it's slipping silently or not slipping at all."

　　"The information is incredibly useful," he added. Whenever the deep part of the fault slips, the stress gets transferred to the shallow part of the fault.

　　"So if all of a sudden, we saw that the deep part of the fault was slipping a huge amount, it might be an indication that there was an increased chance of having an earthquake coming at the shallower part of the fault" he said.

1.What causes tremors and quakes according to the passage?

A.The formation of the Earth, Sun and Moon.

B.The change of the sea levels of the Earth.

C.The effect of the gravitational tug of the sun and moon on the Earth's crust.

D.The movement of creeping in the deep part of the San Andreas Fault.

2.The underlined word "they" in Paragraph 6 refers to 　　　.

A.the researchers

B.the tidal forces

C.the low-frequency earthquakes

D.the typical earthquakes

3.Low-frequency earthquakes occur when 　　　.

A.the tides are getting bigger gradually

B.the sun and moon are in a straight line

C.the sun and moon are 90 degrees apart

D.the San Andreas Fault moves slowly

4.According to Shelly, the most important function of the study is 　　　.

A.to find out where the typical earthquakes occur