Persistent termini of 2004- and 2005-like ruptures of the Sunda megathrust

To gain insight into the longevity of subduction zone segmentation, we use coral microatolls to examine an 1100-year record of large earthquakes across the boundary of the great 2004 and 2005 Sunda megathrust ruptures. Simeulue, a 100-km-long island off the west coast of northern Sumatra, Indonesia, straddles this boundary: northern Simeulue was uplifted in the 2004 earthquake, whereas southern Simeulue rose in 2005. Northern Simeulue corals reveal that predecessors of the 2004 earthquake occurred in the 10th century AD, in AD 1394 ± 2, and in AD 1450 ± 3. Corals from southern Simeulue indicate that none of the major uplifts inferred on northern Simeulue in the past 1100 years extended to southern Simeulue. The two largest uplifts recognized at a south-central Simeulue site—around AD 1422 and in 2005—involved little or no uplift of northern Simeulue. The distribution of uplift and strong shaking during a historical earthquake in 1861 suggests the 1861 rupture area was also restricted to south of central Simeulue, as in 2005. The strikingly different histories of the two adjacent patches demonstrate that this boundary has persisted as an impediment to rupture through at least seven earthquakes in the past 1100 years. This implies that the rupture lengths, and hence sizes, of at least some future great earthquakes and tsunamis can be forecast. These microatolls also provide insight into megathrust behavior between earthquakes, revealing sudden and substantial changes in interseismic strain accumulation rates

Evolutionary model type selection for global surrogate modeling

Due to the scale and computational complexity of currently used simulation codes, global surrogate (metamodels) models have become indispensable tools for exploring and understanding the design space. Due to their compact formulation they are cheap to evaluate and thus readily facilitate visualization, design space exploration, rapid prototyping, and sensitivity analysis. They can also be used as accurate building blocks in design packages or larger simulation environments. Consequently, there is great interest in techniques that facilitate the construction of such approximation models while minimizing the computational cost and maximizing model accuracy. Many surrogate model types exist ( Support Vector Machines, Kriging, Neural Networks, etc.) but no type is optimal in all circumstances. Nor is there any hard theory available that can help make this choice. In this paper we present an automatic approach to the model type selection problem. We describe an adaptive global surrogate modeling environment with adaptive sampling, driven by speciated evolution. Different model types are evolved cooperatively using a Genetic Algorithm ( heterogeneous evolution) and compete to approximate the iteratively selected data. In this way the optimal model type and complexity for a given data set or simulation code can be dynamically determined. Its utility and performance is demonstrated on a number of problems where it outperforms traditional sequential execution of each model type

Losses Associated with Secondary Effects in Earthquakes

The number of earthquakes with high damage and high losses has been limited to around 100 events since 1900. Looking at historical losses from 1900 onward, we see that around 100 key earthquakes (or around 1% of damaging earthquakes) have caused around 93% of fatalities globally. What is indeed interesting about this statistic is that within these events, secondary effects have played a major role, causing around 40% of economic losses and fatalities as compared to shaking effects. Disaggregation of secondary effect economic losses and fatalities demonstrating the relative influence of historical losses from direct earthquake shaking in comparison to tsunami, fire, landslides, liquefaction, fault rupture, and other type losses is important if we are to understand the key causes post-earthquake. The trends and major event impacts of secondary effects are explored in terms of their historic impact as well as looking to improved ways to disaggregate them through two case studies of the Tohoku 2011 event for earthquake, tsunami, liquefaction, fire, and the nuclear impact; as well as the Chilean 1960 earthquake and tsunami event

Studies of nonstructural components in tall mass timber buildings with cross-laminated timber rocking walls

In recent years, the performance-based design methodology is helping to meet objectives for resiliency against natural hazards. Post-tensioned cross-laminated timber (CLT) rocking walls are being developed as a seismic resilient lateral load resisting system for mass timber building construction. However, achieving whole building resiliency heavily depends on the resiliency of nonstructural systems, as they comprise the majority of construction costs and are sensitive to low shaking intensities. Nonstructural components can be drift-sensitive, acceleration-sensitive, or sensitive to both drift and acceleration. The mass timber building integrated with the post-tensioned rocking wall system has some features that can affect all nonstructural components. These buildings are flexible and incur significant inter-story drift without much damage to the structural system. Moreover, a rocking wall can induce impact-related high-frequency acceleration spikes. The current study addresses these concerns by evaluating the dynamic response of mass timber buildings integrated with a post-tensioned rocking wall, proposing and investigating low-damage details of partition walls, and evaluating the structural/non-structural interaction effects of including the stiffness and strength of partition walls response in the simulation of the dynamic response of these types of buildings.Initially, a two-story mass timber building tested at the NHERI@UCSD large high-performance outdoor shake table was studied. Data from this experiment showed that although the high-frequency spikes occurred in post-tensioned CLT rocking walls, they were attenuated in the diaphragm. Moreover, it was shown that modeling assumptions such as flexible diaphragm and wall to diaphragm connection could affect the numerical simulation of accelerations in the rocking walls and floor diaphragms of the mass timber building. Subsequently, a few details aimed to reduce the seismic damage to the partition walls were developed and investigated in a series of experiments performed at the NHERI@Lehigh equipment facility. These experiments showed that bidirectional loading had an insignificant influence on the in-plane resistance of the partition walls, and the overall resistance of the partition walls was trivial compared to the entire sub-assembly. In experiment Phase 1, telescoping detailing (nested or double slip track) was shown to eliminate the damage to the framing at the wall ends compared to traditional slip-track detailing. In Phase 2, including a gap through the corner could eliminate all but cosmetic damage up to more than 2% drift, while including distributed gaps (expansion joints) throughout the wall delayed the onset of damage at the wall intersection to about 1% drift. Finally, structure/nonstructure interaction effects were evaluated in two 5 and 12 story mass-timber buildings integrated with post-tensioned cross-laminated timber rocking walls. Two-dimensional models of representative coupled rocking wall units were developed in OpenSees, and concentrated spring models representing different partition walls with different densities were integrated into these models. Different analyses were performed on the bare rocking wall structure, and the structure integrated with partition walls. Partition walls with classic fixed connection detailing were found to reduce story drift and story shear forces, which can benefit the design of the structure. Partition walls detailed to slip, however, offer little resistance and do not affect the structural response

IMPA versus Cloud Analysis and IDA: Different Methods to Evaluate Structural Seismic Fragility

Well-known methods for seismic performance assessment, such as incremental dynamic analysis (IDA), multi-stripes analysis (MSA) and the cloud method, involve nonlinear response time-history analyses to characterize the relationship between the chosen damage measure versus intensity measure. Over the past two decades, many authors have proposed simplified procedures or nonlinear static approaches to develop fragility. In these procedures, the capacity of the system is evaluated by nonlinear static procedures (i.e., the capacity spectrum method (CSM), the N2 method, modal pushover analysis (MPA)) and the demand is derived by response spectra. In addition to the familiar ones, incremental modal pushover analysis (IMPA) is a novel nonlinear static procedure proposed in recent years, and it is used in this research to present an IM-based fragility estimation. The accuracy and effectiveness of different methods to assess vulnerability are investigated by comparing fragility curves derived by MPA-based cloud analysis, IMPA and cloud analysis against IDA. The comparison gives valuable insights on the influence of scaling on different sets of records; however, a more extended validation is needed to confirm the obtained results and draw more general conclusions. Results arise from two relatively small bins of record motions differing by ranges of Joyner-Boore distance and scattered in a range of magnitude are presented

Spartan Daily March 1, 2011

Volume 136, Issue 18https://scholarworks.sjsu.edu/spartandaily/1125/thumbnail.jp