The Use of a Seismic Database to Analyze Slow Dynamics as a Proxy of Damage

Date: 4/26/2019

Time: 06:00 PM

Room: Grand Ballroom

The passage of seismic waves causes variations in the elastic properties of the medium in which they propagate. These variations can be monitored throughout observables such as the fundamental frequency. When the perturbation arrives, a sudden alteration of the observables is detected, followed by a slow recovery when the wave excitation ends. This recovery is due to a multi-scale relaxation process, known as slow dynamics. Materials that exhibit slow dynamics have in common a small volume of elastically soft constituents distributed within a rigid matrix. This is a system formed by heterogeneities such as cracks, voids, joints between particles, etc., which are responsible for the general elastic behavior of the material. Slow dynamics is a universal phenomenon, i.e. it occurs in many physical systems, and it is observed at laboratory scale, seismological studies and structural response of buildings. Several studies have proved the direct relationship between slow dynamics and the level of heterogeneities, which is closely linked to damage.

We compiled earthquake data recorded in buildings and created a data bank of structural responses. We analyze the fundamental frequency recovery at two scales: after the strongest motion within the recording of one event (short-term recovery), and during long sequences of earthquakes (long-term recovery). Multi-scale relaxation models are applied to our data to study the behavior of different relaxation parameters that are able to characterize both transient and permanent fluctuations of structural state. Our results are compared with those observed in granular materials at laboratory and at the Earth's crust and fault zones.

Despite the difference between scales, conditions and level of complexity, the analogy between results allows us to confirm the universality of the slow dynamics, and its clear connection with the degree of fracturing and mechanical damage in structures. This makes the recovery process following strong seismic deformation an innovative way to monitor structural degradation.

Presenting Author: Ariana L. Astorga

Authors