"I don't get this," Will Jacobs grumbled as he tried to do his fourth-grade science homework.
His mother stepped into the doorway and asked, "Will, are you done with your homework? It's almost time for bed."
"No. I'm still trying to answer these questions.
I just don't understand earthquakes. How can the earth shake?"
"Why don't you take a little break?" Will's mom suggested. "That sometimes helps."
After his mom left, Will set an alarm on his phone.
He had just gotten it for his birthday, and he loved the new gadget.
Will put his head down on the desk and instantly fell asleep.
Soon the alarm went off, making the table vibrate.
Will silenced it, ignoring the message on the phone's screen: "WAKE UP!"
He went back to sleep, only to be woken up again by another vibration.
But this time when Will opened his eyes, he wasn't in his room—he was in a dark, long cave.
And the phone wasn't vibrating—the ground was shaking!
"Whoa," thought Will. "What's going on?"
A voice nearby squeaked, "Alert! Earthquake!"
Will looked around but didn't see anyone. Then he spotted a patch of light on the ground.
He looked closer and saw that it was his phone. The voice came from the device!
Will picked up the phone, mumbling to himself, "This is strange. Phones can't talk!"
"Most phones don't talk, but I am a QT-9000."
He almost dropped it again when the phone replied!
"I can talk and do much more. I'm the smartest phone you'll ever have! You can call me QT."
"Wow!" Will exclaimed. "Can you tell me what's happening? Where am I?"
"My sensors indicate that we are in a cave.
And we just experienced a small earthquake," replied QT.
All of a sudden, the ground started shaking again.
"And this is a big earthquake," QT said as a whole section of the rock wall moved.
Will noticed light coming through a crack in the ceiling.
"I'm getting out of here," he said, stuffing the phone in his pocket. He climbed out to the surface.
Nearby a road had torn in half. Will pulled his phone out and asked, "How can a huge part of the ground move like that?"
A map of the world appeared on QT's screen.
"The surface of the planet, called the crust, is made up of chunks called tectonic plates.
There are 12 large plates and many smaller ones," QT explained.
"The plates float on top of the mantle, a soft layer of rock and other materials.
Underneath the mantle is a layer of liquid metal called the outer core.
And underneath that is the inner core, which is solid metal.
It's very hot at the center of the planet, and the heat escaping from there makes the plates move.
The movement is what causes earthquakes," said QT.
"Oh . . ." Will thought for a moment and then asked, "If the plates are constantly moving, why aren't earthquakes happening all the time?"
"Actually they are! Most are just so small that people don't feel them.
Big earthquakes, like this one, happen when friction stops the edges of the plates from moving for a while.
When they finally break loose, they release all that stored energy, like a spring." QT paused for a second.
"My GPS tells me that we are on the San Andreas Fault, in California."
Will's eyes lit up. "We learned about faults in science class!
A fault is the crack between two plates in the planet's crust!"
Will looked at the road again. "That must be a fault over there."
"Yes, it is. Two plates are sliding past each other here, causing powerful earthquakes.
Faults also often appear by mountains. That's because when two plates come together, their edges can wrinkle and fold to make mountains."
Will scratched his head. "What happens when plates move apart? Do huge holes appear in the ground?"
"No. Right now the places where plates are moving apart are mostly under the ocean.
Down there magma—that's hot, liquid rock—rises from between the plates.
It cools when it touches the cold water, so it hardens and becomes part of the crust," QT explained. "Earthquakes can be very destructive.
If that road over there is destroyed, just imagine what can happen in a city during an earthquake. Actually I'll show you."
"How? We're nowhere near a city," Will pointed out.
"Look at my screen and I'll transport us. I told you I have special skills."
Will gazed down at the screen and saw a street in ruins.
Then everything got dark. A moment later Will found himself in the city!
He was standing in a crowded park.
Will was shocked by the destruction around him.
"I'd better stay here, away from the buildings.
My science teacher said that aftershocks always come after a big earthquake, but we don't know when.
It's dangerous because more parts of the buildings could fall. But where are we?" asked Will.
"This is San Francisco after a magnitude 6.9 earthquake," QT replied.
"The earthquake's epicenter was actually about a hundred kilometers away, but you can see how much power it released."
Will looked confused. "What's an epicenter, and what does magnitude mean?"
"Earthquakes start deep underground. The spot on the surface of the planet above the earthquake is called its epicenter.
Magnitude is the strength of an earthquake.
Each point on the magnitude scale is ten times stronger than the one before, so an 8-point earthquake is ten times stronger than a 7-point.
Can you imagine damage ten times worse than this?"
Will shook his head. "No. This is pretty bad. How do they measure magnitude?
Do they count the buildings that fell or something?"
A jagged line appeared on QT's screen. "People who study earthquakes are called seismologists.
They measure earthquakes with machines called seismographs, which monitor the vibrations in the ground.
Usually the earth doesn't move much, so the waves the seismographs draw are pretty small.
But during an earthquake, the waves get really big.
The size of the waves determines the magnitude."
Suddenly the aftershock came. The ground rumbled and then moved.
Terrified, Will shut his eyes. When the sound passed, he slowly opened his eyes.
To his amazement he was back in his room. His phone was vibrating in his hand; the alarm was going off.
"That was a strange dream . . . ," he muttered, reaching for his pencil.
"But QT sure is cool! And now these homework questions will be a piece of cake!"