Problem 1 Explain why an L4-C seismometer (essentially a 1-second sensor with a velocity transducer) that has its case filled with highly viscous oil has an output voltage that is approximately equal to a constant times ground acceleration.
Hint: typically L4C is critically damped. In this case, damping will be significantly higher (z>>0.7 ÞbÝ). Also, Assume output of sensor is V(t) from eqn 0.5 of these notes.
Problem 2 Find the poles and zeros of seismograph system that has a 20 sec displacement transducer seismometer (70.7% damped) that is driving a 100 sec galvanometer (also 70.7% damped). Sketch the response.
Problem 3 Obtain strong motion data from various large earthquakes:
1999 M7.1 Hector Mine, @ Station HEC
2003 M8.3 Tokachi-Oki, @ Station HKD112
(data is available on the website at richter.uprm.edu/~jclinton/data.html
in ascii format for each event, each channel. Data is unprocessed acceleration, in cm/s/s, with the pre-event mean removed)
using Matlab, plot the acceleration, as well as unfiltered velocity and displacement
what can you say about the magnitudes of acceleration, velocity and displacement for these records? How, is at all, do they relate to earthquake size, distance?
What is the effect of removing trends and means from the records? How about pre-event mean? Do they make the observed records more ÔrealisticÕ?