Semi-automated procedure for windowing time series and computing Fourier amplitude spectra (FAS) for the NGA-West2 database

This document introduces and describes the data processing methods developed for computing Fourier amplitude spectra (FAS) in the NGA-West2 project. The products of this study can be used to estimate high-frequency attenuation, kappa (κ), to estimate site amplification through empirical spectral ratios, as well as to aid in the development of ground-motion models (GMMs) based on FAS. To accommodate different potential user objectives, we selected five time windows in the acceleration time series (noise, P-wave, S-wave, coda, and the entire record) for which we compute the FAS. The processing starts with the time-aligned, instrument-corrected, tapered, and filtered acceleration time series. The proposed window selection method is developed through trial and error, and tested against a range of ground motions with different magnitudes and hypocentral distances from different regions. This document summarizes the steps for window selection and FAS computation, and describes the output data format. This report will be accompanied by the final products of the PEER NGA-West2 Project, namely, the published report describing the database [Ancheta et al. 2013] and the flatfile, which can be downloaded in excel format at: http://peer.berkeley.edu/ngawest2/databases/

Investigation of fractured carbonate reservoirs by applying shear-wave splitting concept

In this study, fracture orientations in carbonate reservoirs were determined using a multicomponent velocity analysis based on shear wave splitting. The analysis is based on the estimated velocities of large seismic events with different polarizations. In a fractured zone with a dominant orientation, weak amplitude split shear events, including shear noise, result in shear waves that are polarized toward the symmetry and anisotropy axes and propagate with a common fast and slow velocity, respectively. Thus, a velocity stack should show high coherency anomalies in directions parallel and orthogonal to the fracture strike. Furthermore, because the analysis is applied locally at a specific depth range, it is less susceptible to the effects of overburden anisotropy and noise. The dominant fracture orientations from carbonate reservoirs of four oilfields were compared to those interpreted from fullbore microimager and core data. Fractures in two offshore reservoirs strike NNE-SSW and NW-SE, which are related to Zagros stress. Fractures in two onshore reservoir strikes NE-SW, while in deeper onshore reservoir fractures are aligned with N-S direction. The findings of this study are promising, particularly for the fractured reservoirs especially those located in Abu Dhabi, which are characterized by high heterogeneity and complex fracture network related to complex tectonic history. In order to obtain geometrical parameters of fractures at seismic scale, it is recommended to implement the analysis adapted in this study after acquiring three component zero-offset vertical seismic profiling.Cited as: Diaz-Acosta, A., Bouchaala, F., Kishida, T., Jouini, M. S., Ali, M. Y. Investigation of fractured carbonate reservoirs by applying shear-wave splitting concept. Advances in Geo-Energy Research, 2023, 7(2): 99-110. https://doi.org/10.46690/ager.2023.02.0

Squeezing Kappa (κ) out of the transportable array: A strategy for using bandlimited data in regions of sparse seismicity

The κ parameter (Anderson and Hough, 1984), and namely its site-specific component (κ0), is important for predicting and simulating high-frequency ground motion. We develop a framework for estimating κ0 and addressing uncertainties under the challenging conditions often imposed in practice: 1. Low seismicity (limited, poor-quality, distant records); 2. Limited-bandwidth data from the Transportable Array (maximum usable frequency 16 Hz); 3. Low magnitudes (ML1.2-3.4) and large uncertainty in stress drop (corner frequency). We cannot resolve stress drop within the bandwidth, so we propose an approach that only requires upper and lower bounds on its regional values to estimate κ0. To address uncertainties, we combine three measurement approaches (acceleration spectrum slope, AS; displacement spectrum slope, DS; broadband spectral fit, BB). We also examine the effect of crustal amplification, and find that neglecting it can affect κ0 by up to 35%. DS estimates greatly exceed AS estimates. We propose a reason behind this bias, related to the residual effect of the corner frequency on κAS and κDS. For our region, we estimate a frequency-independent mean S-wave Q of 900±300 at 9-16 Hz, and an ensemble mean κ0 over all sites of 0.033±0.014 s. This value is similar to the native κ0 of the NGA-West2 ground motion prediction equations, indicating that these do not need to be adjusted for κ0 for use in Southern Arizona. We find that stress drop values in this region may be higher compared to estimates of previous studies, possibly due to trade-offs between stress drop and κ0. For this dataset, the within-approach uncertainty is much larger than the between-approach uncertainty, and it cannot be reduced if the data quality is not improved. The challenges discussed here will be relevant in studies of κ for other regions with band-limited data, e.g., any region where data come primarily from the TA

PEER Arizona strong-motion database and GMPEs evaluation

This report summarizes the products and results of a study on the collection, processing, and analysis of earthquake ground-motions recorded in Arizona at several recording stations within 200 km from the Palo Verde Nuclear Generating Station in central Arizona. The recorded ground motion in Arizona were compiled and processed according to the Pacific Earthquake Engineering Research Center’s (PEER) record-processing standards. Shear wave velocity profiles at ten recording stations were measured through the spectral analysis of surface wave dispersion technique. Additionally, “kappa” a measure of energy dissipation in the top 1 to 2 km of the crust, was estimated by three methodologies. The average κ0 (kappa at zero-kilometer distance) was estimated from all sites as 0.033 sec. Finally, response spectra of the recorded ground motions in Arizona were compared with those predicted by the NGA-West2 ground motion prediction equations at large distances in Arizona. The comparison showed that overall the recorded 5% damped response spectral ordinates were over predicted by the NGA-West2 models by a range of 0-0.35 natural log units for events occurring in Central California, and by a range of 0.2-0.7 natural log units for events occurring in Southern California and the Gulf of California

Liquefaction at Strong Motion Stations and in Urayasu City during the 2011 Tohoku-Oki Earthquake

The 2011 M[subscript W] = 9.0 Tohoku-oki earthquake generated a large number of unique soil liquefaction case histories, including cases with strong ground motion recordings on liquefiable or potentially liquefiable soils. We have compiled a list of 22 strong motion stations (SMS) where surface evidence of liquefaction was observed and 16 SMS underlain by geologically recent sediments or fills where surface evidence of liquefaction was not observed. Pre-earthquake standard penetration test data and borehole shear wave velocity (V[subscript s]) profiles are available for some stations, but critical information, such as grain size distribution and fines plasticity, are often lacking. In the heavily damaged city of Urayasu, we performed post-earthquake cone penetration testing at seven SMS and V[subscript s] profiles, using surface wave methods at 28 additional locations to supplement existing geotechnical data. We describe the liquefaction effects in Urayasu, the available site characterization data, and our initial data interpretations

Engineering Reconnaissance Following the October 2016 Central Italy Earthquakes - Version 2

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. As shown in Figure 1.1, this earthquake sequence occurred in a gap between two earlier damaging events, the 1997 M6.1 Umbria-Marche earthquake to the north-west and the 2009 M6.1 L’Aquila earthquake to the south-east. This gap had been previously recognized as a zone of elevated risk (GdL INGV sul terremoto di Amatrice, 2016). These events occurred along the spine of the Apennine Mountain range on normal faults and had rake angles ranging from -80 to -100 deg, which corresponds to normal faulting. Each of these events produced substantial damage to local towns and villages. The 24 August event caused massive damages to the following villages: Arquata del Tronto, Accumoli, Amatrice, and Pescara del Tronto. In total, there were 299 fatalities (www.ilgiornale.it), generally from collapses of unreinforced masonry dwellings. The October events caused significant new damage in the villages of Visso, Ussita, and Norcia, although they did not produce fatalities, since the area had largely been evacuated. The NSF-funded Geotechnical Extreme Events Reconnaissance (GEER) association, with co-funding from the B. John Garrick Institute for the Risk Sciences at UCLA and the NSF I/UCRC Center for Unmanned Aircraft Systems (C-UAS) at BYU, mobilized a US-based team to the area in two main phases: (1) following the 24 August event, from early September to early October 2016, and (2) following the October events, between the end of November and the beginning of December 2016. The US team worked in close collaboration with Italian researchers organized under the auspices of the Italian Geotechnical Society, the Italian Center for Seismic Microzonation and its Applications, the Consortium ReLUIS, Centre of Competence of Department of Civil Protection and the DIsaster RECovery Team of Politecnico di Torino. The objective of the Italy-US GEER team was to collect and document perishable data that is essential to advance knowledge of earthquake effects, which ultimately leads to improved procedures for characterization and mitigation of seismic risk. The Italy-US GEER team was multi-disciplinary, with expertise in geology, seismology, geomatics, geotechnical engineering, and structural engineering. The composition of the team was largely the same for the two mobilizations, particularly on the Italian side. Our approach was to combine traditional reconnaissance activities of on-ground recording and mapping of field conditions, with advanced imaging and damage detection routines enabled by state-of-the-art geomatics technology. GEER coordinated its reconnaissance activities with those of the Earthquake Engineering Research Institute (EERI), although the EERI mobilization to the October events was delayed and remains pending as of this writing (April 2017). For the August event reconnaissance, EERI focused on emergency response and recovery, in combination with documenting the effectiveness of public policies related to seismic retrofit. As such, GEER had responsibility for documenting structural damage patterns in addition to geotechnical effects. This report is focused on the reconnaissance activities performed following the October 2016 events. More information about the GEER reconnaissance activities and main findings following the 24 August 2016 event, can be found in GEER (2016). The objective of this document is to provide a summary of our findings, with an emphasis of documentation of data. In general, we do not seek to interpret data, but rather to present it as thoroughly as practical. Moreover, we minimize the presentation of background information already given in GEER (2016), so that the focus is on the effects of the October events. As such, this report and GEER (2016) are inseparable companion documents. Similar to reconnaissance activities following the 24 August 2016 event, the GEER team investigated earthquake effects on slopes, villages, and major infrastructure. Figure 1.2 shows the most strongly affected region and locations described subsequently pertaining to: 1. Surface fault rupture; 2. Recorded ground motions; 3. Landslides and rockfalls; 4. Mud volcanoes; 5. Investigated bridge structures; 6. Villages and hamlets for which mapping of building performance was performed

Reconnaissance of 2016 Central Italy Earthquake Sequence

The Central Italy earthquake sequence nominally began on 24 August 2016 with a M6.1 event on a normal fault that produced devastating effects in the town of Amatrice and several nearby villages and hamlets. A major international response was undertaken to record the effects of this disaster, including surface faulting, ground motions, landslides, and damage patterns to structures. This work targeted the development of high-value case histories useful to future research. Subsequent events in October 2016 exacerbated the damage in previously affected areas and caused damage to new areas in the north, particularly the relatively large town of Norcia. Additional reconnaissance after a M6.5 event on 30 October 2016 documented and mapped several large landslide features and increased damage states for structures in villages and hamlets throughout the region. This paper provides an overview of the reconnaissance activities undertaken to document and map these and other effects, and highlights valuable lessons learned regarding faulting and ground motions, engineering effects, and emergency response to this disaster

Shear Modulus Reduction and Damping Ratio Curves for Earth Core Materials of Dams

It is essential to obtain shear modulus reduction and damping ratio curves to perform dynamic analyses of earth cored embankment dams. Many studies have been performed for dynamic properties of clayey soils but it has been limited for earth core materials of dams. This study conducted resonant column tests to obtain G/Gmax and damping ratio (D) curves for 31 specimens (17 undisturbed and 14 remolded specimens) from 13 earth cored embankment dams. Empirical G/Gmax and D curves are proposed for dynamic properties of clayey earth core materials. Fitting curves are provided by using the functional forms of Ramberg-Osgood and Darendeli models. The observation shows that the undisturbed earth cores yield relatively higher G/Gmax and lower D curves than the remolded cores. G/Gmax curves of compacted earth cores are relatively higher than those of Vucetic and Dobry curves for a similar level of plasticity index. Uncertainty and bias are calculated by performing residual analysis, which shows that there is no clear bias in predicting G/Gmax and the uncertainties between undisturbed earth core materials and natural deposits are in a similar level. A proposed empirical relationship of G/Gmax and D curves for earth core materials can be utilized for dynamic analyses of embankment dams in case of lack of in-situ data.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Unified correlation between SPT-N and shear wave velocity for a wide range of soil types considering strain-dependent behavior

The shear wave velocity (Vs) of sediments plays a key role in seismic wave amplification and is required in site response analysis. Such information is usually lacking during field exploration, but standard penetration test blow count (N) is typically available. Therefore, several studies have established empirical correlations between N and Vs for engineering use. However, these empirical correlations significantly vary in terms of model form and are only applicable to specific soil types, such as sand or clay. A unified empirical correlation for a wide range of soil types, which contains several soil properties (e.g., liquid limit and plasticity index (PI)) in addition to the Vs and N of strata, is developed in this study using the Engineering Geological Database for the Taiwan Strong Motion Instrumentation Program. Influences of confining stress, fines content (FC), PI, and soil types on small-strain properties (i.e., Vs) and large-strain measurements (i.e., N) are first evaluated through the developed correlations with these parameters. The unified correlation between Vs and N that is dependent on confining stress, FC, and PI is then proposed through the conditional prediction approach. The model successfully applies to different regions in Taiwan that includes various types of soil deposits and, thus, is potentially used for the other regions