September 5, 2001
Willet Science Center 109
(Overflow to WSC 101 if necessary…)
Abstract: Force-balance instruments, which are the modern standard in seismology, were partly developed to eliminate the effects of creep. Because early instruments used a velocity rather than position detector to do measurements on the test mass, they had poor low-frequency sensitivity. As such, they provided little information concerning slow variations in length of the restoring spring--changes due to creep and creep recovery in response to a varying load. Similarly, newer instruments have yielded little useful information because of their "elimination" of creep through the use of force-feedback. It is not surprising, therefore, that the influence of creep on seismic instruments has been poorly understood. Dr. Peters has spent more than a decade studying creep-related properties of materials at the mesoscale, while developing 'mesodynamics' with his patented capacitive sensor. Studies of chaos and complexity in mechanical systems have caused him to conclude that secondary creep, and not primary creep as commonly believed, is the dominant cause for damping of a freely decaying instrument. Moreover, preliminary experiments suggest the possibility of a counter-intuitive low frequency benefit from creep -- increased instrument sensitivity through a natural mechanism of positive feedback. These claims will be supported with data collected from a unique tiltmeter that he designed, along with simple hardware demonstrations of some conceptually simple nonlinear physics phenomena that relate to the problem.
join us for light refreshments at 4:15.