Abstract
This study focuses on two weak points of the present procedure to carry out microzoning study in near-field areas: (1) the Ground Motion Prediction Equations (GMPEs), commonly used in the reference seismic hazard (RSH) assessment; (2) the ambient noise measurements to define the natural frequency of the near surface soils and the bedrock depth. The limitations of these approaches will be discussed throughout the paper based on the worldwide and Italian experiences performed after the 2009 L’Aquila earthquake and then confirmed by the most recent 2012 Emilia Romagna earthquake and the 2016–17 Central Italy seismic sequence. The critical issues faced are (A) the high variability of peak ground acceleration (PGA) values within the first 20–30 km far from the source which are not robustly interpolated by the GMPEs, (B) at the level 1 microzoning activity, the soil seismic response under strong motion shaking is characterized by microtremors’ horizontal to vertical spectral ratios (HVSR) according to Nakamura’s method. This latter technique is commonly applied not being fully compliant with the rules fixed by European scientists in 2004, after a 3-year project named Site EffectS assessment using AMbient Excitations (SESAME). Hereinafter, some “best practices” from recent Italian and International experiences of seismic hazard estimation and microzonation studies are reported in order to put forward two proposals: (a) to formulate site-specific GMPEs in near-field areas in terms of PGA and (b) to record microtremor measurements following accurately the SESAME advice in order to get robust and repeatable HVSR values and to limit their use to those geological contests that are actually horizontally layered.
Highlights
On April 6, 2009, at 1:32 a.m. an Mw 6.3 earthquake with shallow hypocentral depth (8.3 km) hit the city of L’Aquila and several municipalities within the Aterno Valley
The uncertainty of Ground Motion Prediction Equation (GMPE) in near field areas Several examples of GMPEs are provided in literature (Kramer 1996 among others) while a recent throughout review of several possible formulations of GMPEs used in the USA can be found at the Pacific Earthquake Engineering Research center PEER website http://peer.berkeley. edu/publications/peer_reports_complete.html
Two GMPEs within the first 35 km have been drawn for two ranges of moment magnitude: 5 ≤ Mw1 < 5.5 and 5.5 ≤ Mw2 ≤ 6.5
Summary
On April 6, 2009, at 1:32 a.m. (local time) an Mw 6.3 earthquake with shallow hypocentral depth (8.3 km) hit the city of L’Aquila and several municipalities within the Aterno Valley. (local time) an Mw 6.3 earthquake with shallow hypocentral depth (8.3 km) hit the city of L’Aquila and several municipalities within the Aterno Valley This earthquake can be considered one of the most mournful seismic event in Italy since 1980 its magnitude was moderately-high: 308 fatalities and 60.000 people displaced The pioneering work by Signanini et al (1983) after the 1979 Friuli earthquake confirmed the observations on the ground: local seismic effects could enlarge the referenced hazard at a site by 2–3 times in terms of MCS scale Intensity and in PGA values owing to the local morphological and stratigraphic settings Such RSL is evident in near field areas, from on named NFAs. The NFAs have been defined among others by Boore (2014a) as the Fault Damage Zones. These areas cannot be uniquely identified depending on the source rupture mechanisms, the surficial soil deposits and the multiple calculation methods used for measuring the distance between the (2020) 7:11
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
