EAN consensus statement for management of patients with neurological diseases during the COVID‐19 pandemic

Background and purpose The recent SARS‐CoV‐2 pandemic has posed multiple challenges to the practice of clinical neurology including recognition of emerging neurological complications and management of coexistent neurological diseases. In a fast‐evolving pandemic, evidence‐based studies are lacking in many areas. This paper presents European Academy of Neurology (EAN) expert consensus statements to guide neurologists caring for patients with COVID‐19. Methods A refined Delphi methodology was applied. In round 1, statements were provided by EAN scientific panels (SPs). In round 2, these statements were circulated to SP members not involved in writing them, asking for agreement/disagreement. Items with agreement >70% were retained for round 3, in which SP co‐chairs rated importance on a five‐point Likert scale. Results were graded by importance and reported as consensus statements. Results In round one, 70 statements were provided by 23 SPs. In round two, 259/1061 SP member responses were received. Fifty‐nine statements obtained >70% agreement and were retained. In round three, responses were received from 55 co‐chairs of 29 SPs. Whilst general recommendations related to prevention of COVID‐19 transmission had high levels of agreement and importance, opinion was more varied concerning statements related to therapy. Conclusion This is the first structured consensus statement on good clinical practice in patients with neurological disease during the COVID‐19 pandemic that provides immediate guidance for neurologists. In this fast‐evolving pandemic, a rapid response using refined Delphi methodology is possible, but guidance may be subject to change as further evidence emerges

Robust features of the source process for the 2004 Parkfield, California, earthquake from strong-motion seismograms

We explore a recently developed procedure for kinematic inversion based on an elliptical subfault approximation. In this method, the slip is modelled by a small set of elliptical patches, each ellipse having a Gaussian distribution of slip. We invert near-field strong ground motion for the 2004 September 28 M w 6.0 Parkfield, California, earthquake. The data set consists of 10 digital three-component 18-s long displacement seismograms. The best model gives a moment of 1.21 × 10 18 N m, with slip on two distinct ellipses, one with a high-slip amplitude of 0.91 m located 20 km northwest of the hypocentre. The average rupture speed of the rupture process is ∼2.7 kms -1. We find no slip in the top 5 km. At this depth, a lineation of small aftershocks marks the transition from creeping above to locked below, in the interseismic period. The high-slip patch coincides spatially with the hypocentre of the 1966 M w6.0 Parkfield, California, earthquake. The larger earthquakes prior to the 2004 Parkfield earthquake and the aftershocks of the 2004 earthquake (M w > 3) also lie around this high-slip patch, where our model images a sharp slip gradient. This observation suggests the presence of a permanent asperity that breaks during large earthquakes, and has important implications for the slip deficit observed on the Parkfield segment, which is necessary for reliable seismic hazard assessment. © 2012 The Authors Geophysical Journal International © 2012 RAS

Inversion of the spatiotemporal distribution of early postseismic slip within the rate-and-state framework using high-rate GNSS position time series

International audienceWhereas the spatial and temporal evolution of early postseismic slip (i.e., the first few hours) has been shown to be complex, we do not know well the mechanisms that control its behaviour. One pending question is to know whether or not the rate-and-state friction law is required to explain it, or if the rate-dependent friction law, traditionally used to explain afterslip observations on a day-to-month time scale, is sufficient. Based on 30-sec high-rate position time series that show the early postseismic surface displacements at 13 stations from 2.5 minutes to 3 days after the 2015 M8.3 Illapel, Chile, earthquake, we attempt to infer the frictional properties that control early postseismic slip on the fault. We invert simultaneously for the location and the amplitude of the slip patches, and for the frictional parameters that control their temporal behaviour. We use the elliptic slip patch inversion method (Vallée et Bouchon, 2004; Twardzik et al., 2012) that allows to reduce the number of unknown parameters and we solve, in particular, for the rate-and-state friction law parameters. The obtained frictional parameters are consistent with a velocity-strengthening behaviour. Our first results indicate that 1) the framework can explain the full time series, 2) the postseismic slip patches are located on the edge of the coseismic slip distribution, 3) the obtained stress drop parameter is consistent with that found for the coseismic rupture, and 4) the stiffness of the rate-and-state friction law is consistent with the size of the slip patches. We will also discuss the ability of compatible models to apply at longer postseismic timescales which would suggest a unique underlying physical process

Kinematics of the 2012 Ahar–Varzaghan complex earthquake doublet (Mw6.5 and Mw6.3)

International audienceOn 2012 August 11, an earthquake doublet (Mw6.5 and Mw6.3), separated in time by 11 min, occur in the northwest of Iran. The hypocentres of these earthquakes are close (∼6 km) and located near the cities of Ahar and Varzaghan. The rupture process of both main shocks is retrieved by inverting the near-field strong motions data and using the elliptical subfault approximation method. Our calculations show that the two earthquakes are occurring on two distinct fault planes: the first main shock (M1) has nucleated at a depth of ∼8.5 km, and is located ∼4 km east of the eastern termination of the E-W trending surface rupture. The slip reaches the ground surface west of the hypocentre on an E-W striking fault (N88°E) that dips almost vertically (80°S). This earthquake exhibits a right-lateral strike-slip mechanism. The entire slip is imaged on a single patch that ruptures with an average speed of 2.4 km s−1. The rupture duration is ∼5.6 s and the earthquake releases a seismic moment of ∼8.41E + 18 N·m. The slip reaches the surface with a right-lateral dislocation value of ∼1 m, which is consistent with the observed surface rupture. About 11 min later, the second main shock (M2) nucleates ∼5 km to the west and 4 km to the north with respect to the hypocentre of the M1, and at a depth of ∼16.5 km. The M2 rupture evolves toward shallower depths and to the west on an ENE-WSW oriented fault plane (strike ∼256°) with a dip of ∼60° northward. The slip is essentially distributed on two distinct patches with strike-slip and reverse mechanisms, respectively. The first patch has a pure right-lateral strike-slip mechanism, and ruptures at a relatively fast speed of over 2.8 km s−1, and last for about 2.6 s until it reaches the second patch. The latter has a reverse mechanism (rake∼112°) and extends the rupture toward shallow depths, and to the west at a speed of ∼2.5 km s−1, and its rupture lasts for ∼2.5 s. The top of the slip distribution of M2 stops at a depth of ∼8 km. We observe that aftershocks surround the M1 and most of the M2 slip models. They are not distributed in the region of high slip (∼3.1 m) of M1. We show that the rupture of M2 is controlled by the static Coulomb stress changes caused by M1, with the maximum slip of M2 located in the positive Coulomb stress caused by M1. The M2 rupture stops where it reaches the area of high negative Coulomb stress change (over −10 bars). The cumulative Coulomb stress fields of both main shocks show a transfer of positive static Coulomb stress change of >0.1 bars on the eastern segment of the North Tabriz Fault. This segment did not rupture since the 1721 M∼7.6–7.7 event that has destroyed the city of Tabriz, and that currently hosts 2 million people. The occurrence of this earthquake doublet with different mechanisms reveals the slip partitioning of the oblique convergence regime of NW Iran on the Ahar–Varzaghan complex fault syste