Do you know that you can use your iPhone, iPad or Macbook as a basic seismometer, the same device that is used to measure the magnitude of earthquakes and volcanoes?
OK, try this.
Launch the Safari browser on your iOS device, or Google Chrome if you using a Macbook, and then open this page - isthisanearthquake.com. Now shake your phone /computer and the website will capture these movements in real-time much like a seismograph.
The idea in simple English is something like this. Apple laptops and mobile devices have a built-in accelerometer. As you move the hardware, the changes in the orientation of the device are detected and reported to the browser which then maps this new data into the seismograph.