Earthquake Engineering Research Institute

Reliable knowledge of the crustal properties beneath the North Anatolian fault (NAF), seismically silent for more than 250 years beneath the Marmara Sea (MS), is crucial for understanding seismic hazard and mitigating the potential for disaster on an enormous scale. In the present work, the first three-dimensional inverse modeling performed on a magnetotelluric dataset of the MS has unveiled localized weak and locked fault segments along this shear deformation zone. Low-resistivity regions along the northern branch of the NAF beneath the Central and Çınarcık-Imralı basins are likely attributed to the presence of fluids, which may represent a fault zone conductor in a fractured zone and can explain the densely populated microseismicity. These low-resistivity anomalies surrounded by higher resistivity structures imply that the segmented, multi-branched NAF system extends beneath the MS, following the Intra-Pontide suture zone. The resistive anomalies, between the Central and Çınarcık basins, along with those at the western and eastern extremities of the MS, presumably signify regions of stress accumulation, shedding light on the ongoing processes of fault mechanics at play in this critical region.

Destabilization of volcanic edifices can generate debris avalanches with catastrophic impacts on their environment. We present the first high-resolution muography of Mount Unzen, Japan, conducted to characterize the structure of lava lobes formed on the volcano's summit and flank during the 1990-1995 eruption. A multi-wire-proportional-chamber-based muon tracking system was operated for 203 d. The obtained high-resolution muographic image shows the internal density structure of Mount Unzen with a spatial resolution of 12 m. Mean densities were respectively measured as 2470 and 2290 kg m-3 for the base rock and a fracture zone, and both were consistent with the results of prior drilling and sampling experiments. The mean density of lava lobes was measured significantly lower value of 1570 kg m-3, indicating post-eruptive structural weakening. A comparison between the time-series of muographically measured density-lengths and daily precipitation records suggest that rainfall-induced gravitational destabilization did not occur during the observational period. This work demonstrates that long-term (multi-year) muon monitoring of the lava lobes can provide valuable complementary information for volcanic stability assessments.

Recent extreme expansion of urban sites and infrastructures has intensified flood risks in major cities, raising the ultimate call to strengthen resilience against natural hazards. Thus, this study proposes a comprehensive assessment framework to evaluate flood resilience in urban areas by integrating 12 global and 81 sub-criteria related to socio-economic and urban characteristics. A novel decision-making model under uncertainty, structured on q-rung orthopair fuzzy sets combined with GIS, was developed to capture real-world complexities in resilience analysis of urban floods. Furthermore, the implemented sensitivity analysis experiments confirmed the robustness of the model, with strong consistency observed through correlation tests. The developed approach was applied to a critical district of Tehran, Iran’s capital and the largest city in Western Asia, which is a megacity highly exposed to flooding due to its location across three river basins. Using the weighted criteria, GIS-based resilience maps were generated and classified into five levels of resilience. The results indicate that 78.69% of the study area exhibits moderate or lower resilience, underscoring substantial vulnerability to future floods under shifting climate patterns. Management scenarios have been suggested to mitigate the adverse effects of the floods in urban areas that can be adapted to other flood-prone megacities worldwide.

For many years, steel moment-resisting frames (SMRF) with welded beam-column connections were thought to be the best lateral-force-resisting system for buildings in high-seismic regions. However, the 1994 Northridge earthquake revealed the important vulnerabilities of what are now referred to as pre-Northridge connections, which experienced unanticipated brittle fractures in many buildings in the Los Angeles Metropolitan Region. There are several tall SMRF buildings with pre-Northridge connections worldwide, raising serious safety concerns about their performance during future earthquakes. To investigate possible undiscovered damage in these types of connections, an advanced probabilistic regional seismic risk and damage assessment is conducted on 97 tall SMRF buildings in the Financial District of San Francisco, California, with pre-Northridge beam-column connections that were subjected to the 1989 Loma Prieta earthquake. This study aims to identify the buildings, floor levels, and orientations more likely to have experienced brittle fractures during the Loma Prieta earthquake. Results indicate that despite this earthquake being only moderate in magnitude with an epicenter approximately 95 km away from the Financial District, peak inter-story drift ratios in the tall buildings reach 0.65%. Median peak probabilities of yielding and fracture of beam-column connections do not exceed 37% and 12%, respectively. As a result of ground motion directionality and differences in grid plan in the city, buildings located south of Market Street experienced considerably greater building responses and probabilities of damage than buildings located north of Market Street. Estimates of damage from this study suggest that some pre-Northridge beam-column connections likely fractured during the Loma Prieta earthquake, but the fractures were not as widespread as in the 1994 Northridge earthquake. However, earthquakes with either higher magnitudes or closer source-to-site distances to the city of San Francisco may cause significant damage to SMRF buildings constructed before the Northridge earthquake.

This study investigates the following three issues in numerical models of the thermal structure of subduction zones, using the Tohoku region in Northeast Japan as an example: (1) A steady state is often assumed in models, (2) quantitative assessment of the uncertainty in the predicted temperatures is lacking and (3) surface heat flow has been used to constrain many of the models. I found that, at least under the model setting of this study, a steady state may be safely assumed as long as only surface heat flow within 150 km of the trench is used to constrain the model. I used Bayesian inference to predict the thermal structure, with surface heat flow near the trench and the location of the blueschist-out boundary in the oceanic crust as observational constraints. The depth of slab–mantle kinematic decoupling, effective friction coefficient and rate of radiogenic heat production in the upper island arc crust were constrained simultaneously to be $\sim$80–100 km, 0.03–0.08 and 1.5–2.16 $\mu$W m$^{-3}$, respectively, although the decoupling depth is sensitive to the assumed location and temperature of the blueschist-out boundary. The uncertainties in slab temperature reach $\sim$450 K at depths of $<$100 km and 100 K for greater depths, which are substantial. To reduce these uncertainties, it is necessary to reduce the uncertainty in the input parameters and obtain additional observational constraints.