Question

what is a seismograph and how does it work?

what other methods do scientist use to measure earthquakes

Answer 1

http://science.howstuffworks.com/question142.htm

http://tremor.nmt.edu/faq/how.html

http://pubs.usgs.gov/gip/earthq1/measure.html

http://earthquake.usgs.gov/learning/topics/measure.php