Waveform question

Hi there,

I just wanted to know more about reading waveforms. For example in the image below, the earthquake starts with a downwards spike followed by an upward spike. Some earthquakes though start with an upward spike. What is the meaning and difference between earthquakes starting with an upward/downward spike?

Thank you!

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Hello VS1. I found the info below helpful in understanding what the first motion is indicating:

http://rses.anu.edu.au/~nick/teachdoc/lecture11.pdf (Starting at slide 12)
Focal Mechanisms Explained: What are those “beach balls”? (Educational) - YouTube

–Steve Caron
Chino Hills, Ca


Wow, thanks for this! Really helpful.


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