While initial, blind computations significantly differed from one another, a remarkable fit was obtained after correcting for some nonmethodological errors for four 3D methods: the arbitrary high-order derivative discontinuous Galerkin method (ADER-DGM), the velocity-stress finite-difference scheme on an arbitrary discontinuous staggered grid (FDM), and two implementations of the spectral-element method (SEM1 and SEM2). Their basic formulation is briefly recalled, and their implementation for the Grenoble Valley and the corresponding requirements in terms of computer resources are detailed.

Besides a visual inspection of PGV maps, more refined, quantitative comparisons based on time-frequency analysis greatly help in understanding the origin of differences, with a special emphasis on phase misfit. The match is found excellent below 1 Hz, and gradually deteriorates for increasing frequency, reflecting differences in meshing strategy, numerical dispersion, and implementation of damping properties.

While the numerical prediction of ground motion cannot yet be considered a mature, push-button approach, the good agreement reached by four participants indicates that, when used properly, numerical simulation is actually able to handle correctly wave radiation from extended sources in complex 3D media. The main recommendation to obtain reliable numerical predictions of earthquake ground motion is to use at least two different but comparably accurate methods, for instance the present formulations and implementations of the FDM, SEM, and ADER-DGM.

In this case, due to the saturation of near-source velocimetric instruments, the normalized cross-correlation matrix was calculated considering the first not saturated velocimetric station (ASO2, 108 km northeast to the epicenter), including the same selected portion of signals (on the base of signal-to-noise ratio) related both to the target and to 11 events, with M_L ranging from 2.2 to 3.0, that occurred in the same area. The similarity analysis, performed through the bridging technique, allows us to detect an M_L 2.9 aftershock characterized by a meaningful degree of similarity (70%) compared to the target. Given as a fact that if two events are similar for a far-field station they have to be similar also for a near-source one, it was in this way possible to use the selected aftershock (doublet), recorded in near source to reproduce the target for the saturated near-source stations. The results of the simulations were compared with ground-motion values predicted by empirical ground-motion prediction equations (GMPEs), calibrated using both Italian and European data.

The brittle upper crust in the vicinity of the NMSZ is modeled as a uniform overburden with a horizontal-basal surface, which rests on a horizontal ductile lower crust that is cut by a vertical, northeast-striking right-lateral strike-slip shear zone. We acknowledge that many favorably oriented preexisting faults have been exploited as components of the flower structure. The brittle overburden material is subject to simple shearing stress parallel to the deep-seated lower crustal shear zone, and preexisting faults of the Reelfoot rift system give the upper crust a mechanical anisotropy (planes of weakness striking northeast) that is the correct orientation for development of P shear faults. The deep-seated fault movement deforms the overlying upper crust that controls the structural geometry, the modern seismicity, and the large earthquake sequences in the NMSZ.

The three-dimensional NMSZ model of faulting developed in this study shows that the Bootheel and Big Creek lineaments, inferred to be two subparallel P shear faults rooted in a deep-seated fault in the lower crust, are significant in shaping the geometry of the NMSZ. These series of faults produce a large-scale flower structure in cross section. The proposed NMSZ model uses the intersections of the deep-seated fault and the two subparallel P shear faults for the locations of the 1811 and 1812 earthquakes. The model gives rise to a predictable pattern of surface deformation that is in good agreement with the observed seismicity patterns in the region.

We document selected examples of how the change in magnitude calibration may affect seismicity- and hazard-related analyses that are based on the Southern California Seismic Network (SCSN) catalog. Especially the change of the b-value from ~1.1 to ~0.9 has potentially major implications for hazard related applications.

We investigate the variability of the ground motion as a function of different source parameters (rupture velocity, slip distribution, nucleation point, and source time function), whose values depend on the state of knowledge of the physical model driving the process. The probability density functions of the simulated ground-motion parameters, such as displacement response spectrum and peak ground velocity, are used to identify particular scenarios that match specific engineering requests.

A cylindrical channel embedded in an infinite medium supports two classes of axially symmetric elastic-wave modes, torsional and longitudinal-radial. Torsional modes have rectilinear particle motion tangent to the cylinder surface. Longitudinal-radial modes have elliptical particle motion in planes that include the cylinder axis, with retrograde motion near the axis. The direction of elliptical particle motion reverses with distance from the axis: once for the fundamental mode, twice for the first overtone, and so on. Each mode exists only above its cut-off frequency, where the phase and group speeds equal the shear-wave speed in the infinite medium. At high frequencies, both speeds approach the shear-wave speed in the channel. All modes have minima in their group speeds, which produce Airy phases on seismograms. For shear wave–speed contrasts of a few percent, thought to be realistic for thermal plumes in the Earth, the largest signals are inversely dispersed and have dominant frequencies of about 0.1–1 Hz and durations of 15–30 sec.

There are at least two possible sources of observable plume waves: (1) the intersection of mantle plumes with high-amplitude core-phase caustics in the deep mantle; and (2) ScS-like reflection at the core-mantle boundary of downward-propagating guided waves. The widespread recent deployment of broadband seismometers makes searching for these waves possible.

Field investigations indicate that the length of the surface-rupture zone is only 28 km for the A.D. 180 earthquake, 11 km for the 1609 earthquake, 23 km for the 1927 earthquake, and 5.1 km for the 1954 earthquake, much shorter than that predicted using an empirical equation between moment magnitude (M_w), surface-rupture length (SRL), coseismic displacement (D), maximum displacement (MD), average displacement (AD), and mode value combined displacement statistic (MVCDS): M_w=5.91+0.609log(SRLxD) for strike-slip faults, M_w=5.81+0.653log(SRLxD) for reverse faults, and M_w=6.93+0.82log(ADxMVCDS) for all faults. This may be common for reverse faulting earthquakes worldwide and suggests that trying to estimate magnitudes of past earthquakes from one type of even the most recent surface-rupture data is unreliable and the empirical equations between magnitude, coseismic slip, and surface-rupture length should be applied with caution to seismic hazard assessment on active thrust faults.

We present a methodology based on the use of a minimum 1D model to detect and remove systematic errors in travel-time data by detailed analysis of station delays and observation residuals and apply it to a local earthquake data set from Costa Rica. The determination of the exact nature of detected inconsistencies needs further investigations in each individual case. If the cause of detected systematic errors cannot be determined beyond any doubt and the afflicted data may not be corrected, they must be deleted from the data set. To assess the extent of influence of systematic errors on hypocenter locations and their uncertainties, we present two examples showing the effects of station mislocation.

Alternative models span the m_max ranges from the 1980s Electric Power Research Institute/Seismicity Owners Group (EPRI/SOG) analysis. Results are presented as hazard ratios relative to the USGS national seismic hazard maps. One alternative model specifies m_max equal to moment magnitude 5.0 and 5.5 for the craton and margin, respectively, similar to EPRI/SOG for some sources. For 2% probability of exceedance in 50 years (about 0.0004 annual probability), the strong m_max truncation produces hazard ratios equal to 0.35–0.60 for 0.2-sec spectral acceleration, and 0.15–0.35 for 1.0-sec spectral acceleration. Hazard-controlling earthquakes interact with m_max in complex ways. There is a relatively weak dependence on probability level: hazard ratios increase 0–15% for 0.002 annual exceedance probability and decrease 5–25% for 0.00001 annual exceedance probability. Although differences at some sites are tempered when faults are added, m_max clearly accounts for some of the discrepancies that are seen in comparisons between USGS-based and EPRI/SOG-based hazard results.

The imaginary component of the observed complex COH is separated into roughened and smoothed parts. The root mean square of the roughened imaginary COH (rms(Im)) is an expression of the statistical noise in the observed coherency, while the behavior of the smoothed imaginary COH gives some indication of the distribution of the microtremor wave field. The mean square of residuals (MSR) between observed and theoretical COHs is an indication of the confidence level on the SWV profile interpreted. MSR values evaluated at pairs of sensors of different orientations give some indication of the azimuth distribution of the microtremor wave field and provide some guidelines on the field procedure when using a limited number of sensors to record SPAC observations.

Observed COHs at site KPK demonstrate the importance of recording longer time series to increase the stability of the observed COHs. The increasing level of statistical noise with increasing frequency at site DBL suggests the SPAC method can be used with a single pair of sensors by restricting its upper frequency limit to the first minimum of the COH. Low values of MSR on observed COHs from most pairs of sensors further strengthen that hypothesis. SPAC observations at site RGB give further insights into the capabilities of the SPAC method to evaluate the SWV profile in limited azimuth microtremor wave-field distribution.

We conclude that (1) the peak nonlinear responses due to the modified records and the scaled-real records are similar if the peaks and troughs effects and response spectral shape effects are taken into account adequately in the choice of scaling factors for the real records; and (2) the peak nonlinear responses due to the simulated and modified records are similar. These findings, though obtained based on limited sets of ground-motion records, are in agreement with previous studies and highlight the need for judicious choices in cases involving the scaling of records. The results also suggest that stochastically simulated records may be an appropriate way to capture overall response potential for both linear and nonlinear structural systems, at least over a range of periods from 0.1 to 2 sec.

We analyzed both ground acceleration spectra of the mainshocks and single-station spectral ratios of broadband seismograms in an extended magnitude range (2.7≤M_w≤5.7). Our results show that neither the spectral amplitudes of recorded ground motions nor the spectral ratios can be fit by a high stress-drop source. Instead we find that the observations are consistent with a low stress drop, our best estimates ranging between 6 and 25 bars, in agreement with the relatively long source duration and small coseismic slip.

We interpret the low stress of the 2002 Molise earthquakes in terms of lower energy release mechanisms due to the reutilization of faults reactivated opposite to their original sense of slip.

Estimates of U_seis for the time intervals 0–1999, 1500–1999, and 1964–2006 using historic and instrumental catalogs suggest a considerable seismic slip deficit when compared with the total slip expected from the temporal extrapolation of geodetic measurements. This suggests a recent weakly coupled plate contact and a total slip predominantly accommodated aseismically despite the 365 A.D. event. High seismic activity up to magnitudes of about M_w 6 is found accompanying the aseismic slip at the plate contact.

Investigations of the seismicity distribution hint at a spatial variability of the seismic energy release in the western forearc of the HSZ. Activity in the proximity of the 365 A.D. epicenter is observed to be an order of magnitude larger than toward the northwest between Crete and Peloponnese. This spatiotemporal variability of the seismic energy release and seismic coupling suggests that subregions of the plate contact undergo alternating periods of locking followed by intermediate magnitude events and aseismic sliding. Thus, the behavior of significant portions of the plate contact southwest of Crete may be described as conditionally stable.