Why Earthquakes Threaten Two Major European Cities: Istanbul and Bucharest

Istanbul and Bucharest are major European cities that face a continuing threat of large earthquakes. The geological contexts for these two case studies enable us to understand the nature of the threat and to predict more precisely the consequences of future earthquakes, although we remain unable to predict the time of those events with any precision better than multi-decadal. These two cities face contrasting threats: Istanbul is located on a major geological boundary, the North Anatolian Fault, which separates a westward moving Anatolia from the stable European landmass. Bucharest is located within the stable European continent, but large-scale mass movements in the upper mantle beneath the lithosphere cause relatively frequent large earthquakes that represent a serious threat to the city and surrounding regions

Weak ductile shear zone beneath a major strike‐slip fault: Inferences from earthquake cycle model constrained by geodetic observations of the western North Anatolian Fault Zone

GPS data before and after the 1999 İzmit/Düzce earthquakes on the North Anatolian Fault Zone (Turkey) reveal a preseismic strain localization within about 25 km of the fault and a rapid postseismic transient. Using 3-D finite element calculations of the earthquake cycle in an idealized model of the crust, comprising elastic above Maxwell viscoelastic layers, we show that spatially varying viscosity in the crust can explain these observations. Depth-dependent viscosity without lateral variations can reproduce some of the observations but cannot explain the proximity to the fault of maximum postseismic velocities. A localized weak zone beneath the faulted elastic lid satisfactorily explains the observations if the weak zone extends down to midcrustal depths, and the ratio of relaxation time to earthquake repeat time ranges from ~0.005 to ~0.01 (for weak-zone widths of ~24 and 40 km, respectively) in the weakened domain and greater than ~1.0 elsewhere, corresponding to viscosities of ~1018 ± 0.3 Pa s and greater than ~1020 Pa s. Models with sharp weak-zone boundaries fit the data better than those with a smooth viscosity increase away from the fault, implying that the weak zone may be bounded by a relatively abrupt change in material properties. Such a change might result from lithological contrast, grain size reduction, fabric development, or water content, in addition to any effects from shear heating. Our models also imply that viscosities inferred from postseismic studies primarily reflect the rheology of the weak zone and should not be used to infer the mechanical properties of normal crust

Documentation of individualized preoperative risk assessment: a multi-center study

Background: Individual surgical risk assessment (ISRA) enhances patient care experience and outcomes by informing shared decision-making, strengthening the consent process, and supporting clinical management. Neither the use of individual pre-surgical risk assessment tools nor the rate of individual risk assessment documentation is known. The primary endpoint of this study was to determine the rate of physician documented ISRAs, with or without a named ISRA tool, within the records of patients with poor outcomes. Secondary endpoints of this work included the effects of age, sex, race, ASA class, and time and type of surgery on the rate of documented presurgical risk. / Methods: The records of non-obstetric surgical patients within 22 community-based private hospitals in Arizona, Colorado, Nebraska, Nevada, and Wyoming, between January 1 and December 31, 2017, were evaluated. A two-sample proportion test was used to identify the difference between surgical documentation and anesthesiology documentation of risk. Logistic regression was used to analyze both individual and group effects associated with secondary endpoints. / Results: Seven hundred fifty-six of 140,756 inpatient charts met inclusion criteria (0.54%, 95% CI 0.50 to 0.58%). ISRAs were documented by 16.08% of surgeons and 4.76% of anesthesiologists (p < 0.0001, 95% CI −0.002 to 0.228). Cardiac surgeons documented ISRAs more frequently than non-cardiac surgeons (25.87% vs 16.15%) [p = 0.0086, R-squared = 0.970%]. Elective surgical patients were more likely than emergency surgical patients (19.57 vs 12.03%) to have risk documented (p = 0.023, R-squared = 0.730%). Patients over the age of 65 were more likely than patients under the age of 65 to have ISRA documentation (20.31 vs 14.61%) [p = 0.043, R-squared = 0.580%]. Only 10 of 756 (1.3%) records included documentation of a named ISRA tool. / Conclusions: The observed rate of documented ISRA in our sample was extremely low. Surgeons were more likely than anesthesiologists to document ISRA. As these individualized risk assessment discussions form the bedrock of perioperative informed consent, the rate and quality of risk documentation must be improved

Structure of the northwestern North Anatolian Fault Zone imaged via teleseismic scattering tomography

Information on fault zone structure is essential for our understanding of earthquake mechanics, continental deformation and seismic hazard. We use the scattered seismic wavefield to study the subsurface structure of the North Anatolian Fault Zone (NAFZ) in the region of the 1999 İzmit and Düzce ruptures using data from an 18-month dense deployment of seismometers with a nominal station spacing of 7 km. Using the forward- and back-scattered energy that follows the direct P-wave arrival from teleseismic earthquakes, we apply a scattered wave inversion approach and are able to resolve changes in lithospheric structure on a scale of 10 km or less in an area of about 130 km by 100 km across the NAFZ. We find several crustal interfaces that are laterally incoherent beneath the surface strands of the NAFZ and evidence for contrasting crustal structures either side of the NAFZ, consistent with the presence of juxtaposed crustal blocks and ancient suture zones. Although the two strands of the NAFZ in the study region strike roughly east–west, we detect strong variations in structure both north–south, across boundaries of the major blocks, and east–west, parallel to the strike of the NAFZ. The surface expression of the two strands of the NAFZ is coincident with changes on main interfaces and interface terminations throughout the crust and into the upper mantle in the tomographic sections. We show that a dense passive network of seismometers is able to capture information from the scattered seismic wavefield and, using a tomographic approach, to resolve the fine scale structure of crust and lithospheric mantle even in geologically complex regions. Our results show that major shear zones exist beneath the NAFZ throughout the crust and into the lithospheric mantle, suggesting a strong coupling of strain at these depths