USE OF AN INEXPENSIVE SEISMOGRAPH TO STUDY LOCAL AND DISTANT EARTHQUAKES

An earthquake that is within 1,000 km (10°) is considered a local earthquake and earthquakes greater than 1,000 km are distant earthquakes (teleseisms). Local earthquakes are detected best by using short period (1 sec) seismometers since the waves are predominantly short period while distant earthquakes are best detected by using long period (10 – 70 sec) seismometers since the waves are mostly long period. The recent August 23, 2011, Virginia earthquake was a local earthquake recorded at Potsdam, NY since its distance was 783 km while a recent earthquake at Costa Rica is a distant event since its distance from Potsdam is 3,900 km. These two local and distant earthquakes were recorded equally well by our simple and inexpensive AS1 seismograph.

The AS1 seismograph that detected these earthquakes produced excellent quality seismograms of the events even though distance varied by 3,153 km. The fact that the AS1 detects local as well as distant earthquakes makes it useful for teaching principles of seismology. Phases that can be seen on local events such as Pg, Sg, Pn, and Sn can be identified and P, S, and surface waves from distant events are identifiable.

The Amaseis software that was downloaded from SUNY Binghamton can also be used to evaluate a Fourier Transform. Studies of the Fourier Transforms of distant and local earthquakes can be compared to compute cut-off frequency and calculate source parameters, stress drop, seismic moment magnitude, and source radius.

In summary, because of its simplicity and low cost of the ASI and its applications in teaching and research, the AS1 is a valuable tool to have for the study of both local and distant earthquakes.