Title: Does seismic moment release process bear imprints of the nucleation mechanisms of deep earthquakes?

Abstract:

The generation of earthquakes at depths exceeding 60 km remains debated, as rocks at such depths are anticipated to be ductile. Seismological investigations have revealed a variety of rupture characteristics that are distinguishable between shallow (0–60 km), intermediate-depth (60–300 km) and deep-focus (300–700 km) earthquakes, and tend to attribute them to different nucleation mechanisms. Here, we apply machine learning classification to a global database of earthquakes with moderate to large moment magnitudes to show that depth-dependent elastic properties can explain the range of resulting rupture characteristics. We find that the rigidity of the surrounding medium is the primary control of almost all the depth-varying earthquakes’ source characteristics, suggesting that seismic moment release process bear few imprints of the nucleation mechanisms of deep and shallow earthquakes. Our results support a previously identified constant strain drop hypothesis, in which the ratio of coseismic slip to the characteristic rupture length remains largely unchanged for earthquakes at all depths and regardless of the nucleation mechanisms. These results also suggest that rigidity-corrected self-similarity holds for earthquakes of different depths and nucleation mechanisms.

Title: Seismic Considerations of Non-Structural Elements in Buildings

Abstract:

Due to their large contribution to building costs, and to safety risks linked to their failure, non-structural elements (NSEs) represent a popular topic, both in research and industry. In general, NSEs (mechanical, architectural, electrical) can be sensitive to accelerations, deformations, or both. The main focus of the seminar will be on acceleration-sensitive NSEs, whose response represents a major concern during earthquake actions.

The seismic design and evaluation of acceleration-sensitive NSEs are commonly performed by using floor response (acceleration) spectra (FRS). The FRS concept was introduced in early 1970s for the design of NSEs in the nuclear industry. The concept is based on a separate (uncoupled) analysis of a building structure and an NSE, meaning that their dynamic interaction is neglected. Such an approach is sufficiently accurate in cases of NSEs whose mass is significantly smaller than that of the building structure. FRS are influenced by ground motion, building, and NSE properties, and they can be “accurately” determined by performing a response history analysis (RHA). However, since the RHA is time-consuming, it is only exceptionally used. In everyday design practice an approximate approach is usually applied, and FRS are determined directly from ground motion spectra.

The general applicability of the FRS concept on buildings has been recognized relatively recently. It currently attracts significant attention of researchers and engineers, which is reflected through an exponential growth of FRS-related articles. The most important research results have been continuously implemented in the seismic design standards, whose notable improvement has been observed lately. On the other hand, there are conceptual differences in the design provisions, which often lead to inconsistent results. Such differences are present in the latest European and US seismic design standards (Eurocode 8 and ASCE 7-22, respectively), and are outlined and discussed in the seminar presentation.