RESUMO
The rupture process of the recent moderate-to-large earthquakes in the Zagros area along the Iran plateau is investigated by analysing the strong motion data provided by the Iranian Building and Housing Research Centre (BHRC). The selected dataset includes the largest and deadliest 2017 Mw 7.3, Iran-Iraq (Ezgeleh) earthquake. The earthquake source parameters (moment magnitude, rupture duration and length, average slip, and static stress drop) are determined using a time-domain, parametric modelling technique based on the time evolution of the P-wave displacement signals. The earthquake source parameters are calculated from simulated triangular moment-rate functions assuming the circular source models for a constant rupture velocity. The anelastic attenuation effect is modelled through the independent frequency-Q parameter ranging from 50 to 200 and accounted for by a post-processing procedure that retrieves the attenuation-corrected, moment-rate triangular shape. Results show that the average static stress-drop with different [Formula: see text], varies between <Δσ> = 0.9 (0.7-1.2) MPa and <Δσ> = 1.6 (1.2-2.0) MPa. Overall, in this research, the rupture radius/length empirically scales with the seismic moment with a self-similar, near-constant stress drop of about 1 MPa. Assuming a circular rupture model for the Ezgeleh earthquake, we estimate a moment magnitude of 6.9, rupture duration of 7 s, source radius of 16 km, average slip of about 2 m and static stress drop of 3.4 MPa.
RESUMO
Complex interaction of rheologically contrasting layers within the lithosphere during the collision of continental plates leads to active faulting, which represents a serious hazard to the population and infrastructure. One of the collision scenarios presumes the existence of a middle-lower crustal channel composed of subducted silicic upper crustal rocks, which is thought to exist in the Tibetan-Himalayan system. Based on the results of seismic tomography, we argue that a similar mechanism of crustal channeling takes place beneath the Zagros mountain system in southwestern Iran. The 3D seismic velocity model reveals an inverted crustal architecture of the collision zone, in which the low-velocity felsic (granitic and sedimentary) upper crustal rocks of the Arabian plate form a seismically inactive lower crustal channel below the higher-velocity mafic (basaltic) middle-upper crustal layer of the Iranian crust. Based on existing numerical models, we suggest that the formation of the felsic channel is likely governed by separation (delamination) of the weak felsic upper crust of the subducting Arabian lithosphere and its ductile underplating under rheologically stronger upper-middle crust of the Iranian plate.
RESUMO
BACKGROUND: The World Health Organisation (WHO) recommends parasitological diagnosis of malaria before treatment, but use of malaria rapid diagnostic tests (mRDTs) by community health workers (CHWs) has not been fully tested within health services in south and central Asia. mRDTs could allow CHWs to diagnose malaria accurately, improving treatment of febrile illness. METHODS: A cluster randomised trial in community health services was undertaken in Afghanistan. The primary outcome was the proportion of suspected malaria cases correctly treated for polymerase chain reaction (PCR)-confirmed malaria and PCR negative cases receiving no antimalarial drugs measured at the level of the patient. CHWs from 22 clusters (clinics) received standard training on clinical diagnosis and treatment of malaria; 11 clusters randomised to the intervention arm received additional training and were provided with mRDTs. CHWs enrolled cases of suspected malaria, and the mRDT results and treatments were compared to blind-read PCR diagnosis. RESULTS: In total, 256 CHWs enrolled 2400 patients with 2154 (89.8%) evaluated. In the intervention arm, 75.3% (828/1099) were treated appropriately vs. 17.5% (185/1055) in the control arm (cluster adjusted risk ratio: 3.72, 95% confidence interval 2.40-5.77; p < 0.001). In the control arm, 85.9% (164/191) with confirmed Plasmodium vivax received chloroquine compared to 45.1% (70/155) in the intervention arm (p < 0.001). Overuse of chloroquine in the control arm resulted in 87.6% (813/928) of those with no malaria (PCR negative) being treated vs. 10.0% (95/947) in the intervention arm, p < 0.001. In the intervention arm, 71.4% (30/42) of patients with P. falciparum did not receive artemisinin-based combination therapy, partly because operational sensitivity of the RDTs was low (53.2%, 38.1-67.9). There was high concordance between recorded RDT result and CHW prescription decisions: 826/950 (87.0%) with a negative test were not prescribed an antimalarial. Co-trimoxazole was prescribed to 62.7% of malaria negative patients in the intervention arm and 15.0% in the control arm. CONCLUSIONS: While introducing mRDT reduced overuse of antimalarials, this action came with risks that need to be considered before use at scale: an appreciable proportion of malaria cases will be missed by those using current mRDTs. Higher sensitivity tests could be used to detect all cases. Overtreatment with antimalarial drugs in the control arm was replaced with increased antibiotic prescription in the intervention arm, resulting in a probable overuse of antibiotics. TRIAL REGISTRATION: ClinicalTrials.gov, NCT01403350 . Prospectively registered.
