Paolo Zimmaro

VS30 Empirical Prediction Relationships Based on a New Soil‐Profile Database for the Beijing Plain Area, China

Earthquake ground‐motion prediction models usually define site conditions based on the time‐averaged shear‐wave velocity in the upper 30xa0m ( V S 30). Proxy‐based estimations of V S 30 are commonly used, if velocity measurements are not available. We compile a soil‐profile database for the Beijing plain area (China), using data from research documents and technical reports. The database contains 479 soil profiles, 463 of which have depths greater than 30xa0m. We develop regional relationships for the Beijing plain area for extrapolating the time‐averaged shear‐wave velocity to a given depth less than 30xa0m to V S 30, and then compare the performance of available models. We find that the second‐order polynomial model (Boore etxa0al. , 2011), based on data from Japan, provides an overprediction, whereas the linear model (Boore, 2004) calibrated on data from California underestimates V S 30.nnWe develop relationships for estimating V S 30 based on proxies such as ground slope gradients from radar‐derived digital elevation models (DEMs) and surface geology at different scales. We find that local V S 30 data in the Beijing plain are generally lower than existing 30 arcsec gradient‐based global models. Regression results show a modest correlation between V S 30 and topographic ground slope for several DEM resolutions (3, 15, 30, and 60xa0arcsec). Geology‐based proxies are more effective than ground slope for V S 30 estimation in the analyzed area. We propose a bilinear model based on geologic ages and depositional environments for estimating V S 30, which shows a statistically significant trend for application in the Beijing plain area.nnOnline Material: Figures showing topographic ground slopes and correlations of V S 30 with topographic slope from digital elevation model (DEM) data and a table summarizing data from the 463 boreholes.

Active Faulting in Source Region of 2016–2017 Central Italy Event Sequence

The Central Italy earthquake sequence produced three main shocks: M6.1 24 August, M5.9 26 October, and M6.5 30 October 2016. Additional M5–5.5 events struck this territory on 18 January 2017 in the Campotosto area. Fault plane solutions for the main shocks exhibit normal faulting (characteristic of crustal extension occurring in the inner central Apennines). Significant evidence, including hypocenter locations, strike and dip angles of the moment tensors, inverted finite fault models (using GPS, interferometric aperture radar, and ground motion data), and surface rupture patterns, all point to the earthquakes having been generated on the Mt. Vettore–Mt. Bove fault system (all three main shocks) and on the Amatrice fault, in the northern sector of the Laga Mountains (portion of 24 August event). The earthquake sequence provides examples of both synthetic and antithetic ruptures on a single fault system (30 October event) and rupture between two faults (24 August event). We describe active faults in the region and their segmentation and present understanding of the potential for linkages between segments (or faults) in the generation of large earthquakes.

Local site effects and incremental damage of buildings during the 2016 Central Italy earthquake sequence

The Central Italy earthquake sequence initiated on 24 August 2016 with a moment magnitude M6.1 event, followed by two earthquakes (M5.9 and M6.5) on 26 and 30 October, caused significant damage and loss of life in the town of Amatrice and other nearby villages and hamlets. The significance of this sequence led to a major international reconnaissance effort to thoroughly examine the effects of this disaster. Specifically, this paper presents evidences of strong local site effects (i.e., amplification of seismic waves because of stratigraphic and topographic effects that leads to damage concentration in certain areas). It also examines the damage patterns observed along the entire sequence of events in association with the spatial distribution of ground motion intensity with emphasis on the clearly distinct performance of reinforced concrete and masonry structures under multiple excitations. The paper concludes with a critical assessment of past retrofit measures efficiency and a series of lessons learned as per the behavior of structures to a sequence of strong earthquake events.

Reconnaissance of geotechnical aspects of the 2016 Central Italy earthquakes

Between August and November 2016, three major earthquake events occurred in Central Italy. The first event, with M6.1, took place on 24 August 2016, the second (M5.9) on 26 October, and the third (M6.5) on 30 October 2016. Each event was followed by numerous aftershocks. The 24 August event caused massive damages especially to the villages of Arquata del Tronto, Accumoli, Amatrice, and Pescara del Tronto. In total, there were 299 fatalities, generally from collapses of unreinforced masonry dwellings. The October events caused significant new damage in the villages of Visso, Ussita, and Norcia, although not producing fatalities, since the area had largely been evacuated. The Italy–US Geotechnical Extreme Events Reconnaissance team investigated earthquake effects on slopes, villages, and major infrastructures. The approach adopted to carry out post-earthquake reconnaissance surveys was to combine traditional reconnaissance activities of on-ground evidences and mapping of field conditions with advanced imaging and damage detection routines enabled by state-of-the-art geomatics technology. Presented herein are the outcomes of the post-event reconnaissance surveys conducted after both the August main shock and the October events, focusing on geotechnical aspects, such as earthquake-triggered slope failures, mud volcanoes, performance of different geotechnical structures (i.e., dams, retaining walls, rockfall barriers, road embankments) and building damage patterns related to site amplification.

Correction to: Reconnaissance of geotechnical aspects of the 2016 Central Italy earthquakes

Because of an error during the editorial process the first name initial of author Ernesto Ausilio was incorrectly given as A. (A. Ausilio) in the initial online publication. It should obviously be E. Ausilio. The original article has been corrected.

Rupture Directivity Effects on Strong Ground Motion during the 15 April 2016 Mw 7.0 Kumamoto Earthquake in Japan

Abstract The M w xa07.0 Kumamoto, Japan, earthquake occurred on 15 April 2016 at 16:25 UTC. Using ground accelerations recorded by 104 near‐field stations, we investigate spatial variability of observed ground motions, apparent period dependence, and azimuthal variation, as well as rupture directivity effects on various intensity measures. We develop a simplified ground‐motion model that includes both geometric and anelastic attenuation terms. Comparisons of observed and predicted ground motions suggest that predictions from the Next Generation Attenuation‐West2 models provide good fits for the overall observation. Analysis of spatial distribution of the residuals shows that observed peak ground velocity (PGV) and long‐period spectral accelerations (SAs) in the 150°–180° azimuth range along the rupture backward direction (southwest of the fault) can be as low as 0.3–0.8 times the average observation of this event. Long‐period ground motions on the northeast side of the fault in the forward direction are much higher than average, with PGV and long‐period SAs ranging from 1.2 to 1.5 times the average. There is clear period dependence of the strong ground motion variation. The biases due to directivity generally decrease with decreasing period for all azimuth ranges. On the distance dependence of directivity effects, our study shows that directivity effects can be considered practically nonsignificant for stations close to the hypocenter. We also perform a log–linear regression of the residuals, using a new directivity predictor. Our results show that for the 2016 M w xa07.0 Kumamoto earthquake, rupture directivity produces significant amplifications in the rupture forward direction, whereas deamplification effects are observed in the rupture backward region. Directivity effects are particularly relevant for PGV and long‐period SA (i.e., SA at periods ≥2.0u2009u2009s). Such effects do not have systematic influence on peak ground acceleration and short‐period ground motions (i.e., SA at periods Electronic Supplement: Figures of variation of regression residuals with R rup for observed peak ground acceleration (PGA), peak ground velocity (PGV), and spectral accelerations (SAs) and of regression residuals versus V S 30 .