Broadband Strong-Motion Prediction for Future Nankai-Trough Earthquakes Using Statistical Green’s Function Method and Subsequent Building Damage Evaluation

We used the Green’s function summation method together with the randomly perturbed asperity sources to sum up broadband statistical Green’s functions of a moderate-size source and predict strong ground motions due to the expected M8.1 to 8.7 Nankai-Trough earthquakes along the southern coast of western Japan. We successfully simulated seismic intensity distributions similar to the past earthquakes and strong ground motions similar to the empirical attenuation relations of peak ground acceleration and velocity. Using these results, we predicted building damage by non-linear response analyses and find that at the regions close to the source, as well as regions with relatively thick, soft sediments such as the shoreline and alluvium valleys along the rivers, there is a possibility of severe damage regardless of the types of buildings. Moreover, the predicted damage ratios for buildings built before 1981 are much higher than those built after because of the significant code modifications in 1981. We also find that the damage ratio is highest for steel buildings, followed by wooden houses, and then reinforced concrete buildings.

Probabilistic seismic hazard analysis for Northern Tanzania Divergence Region and the adjoining areas

This paper presents the seismic hazard levels for the Northern Tanzania Divergence (NTD) and adjoining areas by using area seismic source zones. The 15 source zones were considered based on the major geological and tectonic features, faulting style, and seismicity trends. For each source, earthquake recurrence parameters were computed by using the earthquake catalogue with events compiled from 1956 to 2011. The peak ground accelerations (PGA) and spectral accelerations (SA) at 0.2 and 2.0 second, respectively, were computed for a 10% probability of exceedance in 50 years at sites defined by a 0.1° x 0.1° grid. The recurrence parameters of 15 zones and attenuation relations developed by Akkar et al. (2014) and Chiou and Youngs (2014) were integrated in a logic tree. Obtained results that are presented as hazard maps show strong spatial variations ranging from 60 to 330 cm/s/s for PGA, from 100 to 650 cm/s/s at 0.2 sec and from 6 to 27 cm/s/s at 2 sec for 475 years mean return period and 5% damping. Hazard levels depict the general tectonic setting of the study area with the western (Eyasi-Wembere) and central (Natron-Manyara-Balangida) rift segments having relatively high PGA values compared with the eastern Pangani rift. This work provides indications of seismic hazards to policymakers and planners during planning and guidelines for earthquake-resistant design engineers. Keywords: Homogeneous Earthquakes Catalogue; GMPE; PSHA; NTD

Structure and QP–QS Relations in the Seattle and Tualatin Basins from Converted Seismic Phases

ABSTRACT We use converted body-wave phases from local earthquakes to constrain depth to basement and average attenuation relations for the Seattle basin in Washington and the Tualatin basin in Oregon. P-, P-to-S-(Ps), S-to-P-(Sp), and S-wave arrivals are present in three-component recordings of magnitude 2.5–4.0 earthquakes at seismic stations located in these basins. Based on their relative travel times, these phases are attributed to body-wave conversions at the basement-to-basin contact or to high-impedance interfaces within the basins. Depth to basement values are calculated using the differential travel times between direct and converted phases, as well as average P- and S-wave velocity values. We also identify a high-impedance layer in the Tualatin basin that likely represents a laterally extensive deposit of volcanic materials embedded between the basement contact and the Columbia River Basalt Group. In addition, the average QP–QS attenuation relation is calculated for each station by taking the spectral ratio of converted phases to their parent body-wave arrivals. For the Seattle basin, our analysis yields an average QP value of 73 and an average QS value of 60 for seismic waves with frequencies between 2 and 25 Hz. In the Tualatin basin, a much reduced QP–QS relation suggests that average body-wave attenuation is likely higher than in the Seattle basin. The converted phase techniques presented here provide a reliable way to develop estimates of basin depth and attenuation structure for undercharacterized regions using simple passive source seismic records.

Three-dimensional shear-wave quality factor, Qs(f), model for south-central Gulf of California, Mexico obtained from inversion of broadband data

We apply an iterative inversion scheme, initially developed by Hashida and Shimazaki (1984) and later modified by Joshi et al., (2010), to estimate three - dimensional shear - wave quality factor, Qs(f), of south-central Gulf of California, Mexico. An area of 230 km x 288 km in this region is divided into 108 rectangular blocks of different Qs(f). We use 25 well-located earthquakes recorded at three broadband stations of the regional network RESBAN operated by CICESE (Centro de Investigación Científica y de Educación Superior de Ensenada, Baja California) and three Ocean Bottom Seismographs (OBS) of the Sea of Cortez Ocean Bottom Array (SCOOBA) experiment. This dataset permits us to obtain Qs(f) estimates of different blocks using the modified inversion algorithm. Qs(f) is obtained at various frequencies in 0.16 - 7.94 Hz range. We found that the estimated Qs structure correlates with geological and tectonic models of the region proposed in previous studies. A regional frequency-dependent relation using all 1944 values of shear-wave quality factor is obtained at 18 different frequencies in all blocks can be approximated by a function of the form Qs(f) = 20 f 1.2. This relation is typical in a tectonically active region with high S-wave attenuation and is similar to attenuation relations reported by other authors for the Imperial Valley, California region.

Assessment of a polymeric composite as a radiation attenuator and a restoration mortar for cracking in biological shields

This work is dedicated to figuring out robust epoxy/magnetite/boron carbide (EP/Mag/B4C) composite for radiation attenuation at multiple applications related to nuclear installations, as well as restoration mortar for cracking developed in concrete biological shields. The mechanical properties (flexural, compressive, and impact strengths) and the physical properties (water absorption, porosity, and dry bulk density), each, have been performed to label the composite integrity for practical application. In practice, attenuation properties have been performed by using a collimated beam emitted from spontaneous fission 252Cf (100 μg) neutron source and neutron gamma spectrometer with stilbene scintillator. The pulse shape discrimination technique which would come of the zero cross over method was used to measure the fast neutron and gamma-ray spectra. Thermal neutron fluxes have been measured by using the thermal neutron detection system and the BF-3 detector. The attenuation parameters: precisely, macroscopic effective removal cross-sections ΣR (cm-1), macroscopic cross-sections Σ (cm-1), and total attenuation coefficients μ (cm-1) of fast and thermal neutrons and total gamma-rays respectively were evaluated using the attenuation relations. Also, the MCNP5 code and MERCSF-N program have been used to compute the parameters theoretically. When applicable, measured and calculated results were compared, and it tells us a comprehensive agreement.

Catalog of Preinstrumental Earthquakes in Central Mexico: Epicentral and Magnitude Estimations Based on Macroseismic Data

ABSTRACT We present the first parametric catalog of historical earthquakes in Mexico from 1469 to 1912 composed of 323 historical earthquakes. The historical earthquakes were assigned to specific seismotectonic provinces, and attenuation relations of seismic intensity versus distance were calculated using instrumental earthquakes. The intensity data were inverted using a linear regression for the best-fitting magnitude and source location. From the 323 events identified in the historical record, magnitude and source location were determined for 40 earthquakes from 1568 to 1912. The historical subduction earthquakes are distributed uniformly along the coast. There is, however, a conspicuous absence of subduction earthquakes where the great 1985 Michoacán earthquakes took place. The data also show a large number of earthquakes Mw>7 in the presumed Guerrero gap in the past 320 yr. The source parameters of in-slab earthquakes were obtained for 10 earthquakes that took place in the nineteenth and early twentieth centuries. The analysis of completeness of the historical and instrumental International Seismological Centre-Global Earthquake Model catalogs of subduction earthquakes Mw>7.0 show similar values of the slope of the Gutenberg–Richter relation between 1.62 and 1.95. The large b-values appear to reflect the apparently anomalous large number of earthquakes in the magnitude range Mw 7.4–7.7 and an absence of events Mw∼7. This magnitude distribution suggests that the seismicity in the Mexican subduction zone is dominated by characteristic earthquakes in the magnitude range Mw 7.4–7.7, with larger earthquakes Mw>8 showing longer recurrence times. The catalog of historical subduction earthquakes appears to be complete for Mw>7.5. The catalog of crustal earthquakes in the Trans-Mexican volcanic belt is complete since 1568 for events Mw>6.4. Completeness of the catalog of in-slab earthquakes was not estimated due to the short record for this type of event.

The 1885 M 6.9 Earthquake in the French Guiana–Brazil Border: The Largest Midplate Event in the Nineteenth Century in South America

In 4 August 1885, 06:30 local time, a strong earthquake (reported intensities up to VI–VII modified Mercalli intensity [MMI]) was felt in the French Guiana, causing slight damage. Recently discovered newspaper records show that this event was also felt as far as Georgetown (British Guyana), Belém, and several other localities along the Amazon River toward Manaus (Brazil). The distribution of intensities and the radius of the felt area indicate a magnitude around Mw 6.9, which makes it the largest known earthquake in the stable continental region of South America, since the nineteenth century. The epicenter, determined with four different attenuation relations, lies onshore near the border between the French Guiana and Brazil, although an epicenter offshore in the continental slope cannot be ruled out with 95% confidence. The epicenter (03.4° N, 52.9°W±100 km) likely lies in the Transamazonian (2.2–2.0 Ga) geochronological province in the Guyana shield of the Amazon craton. No nearby failed rift is known onshore near the epicenter, which would place this event in the ∼30% class of nonextended stable continental crust. Other nearby smaller earthquakes (both historical and instrumental) with magnitudes up to mb 5.2, indicate a cluster of seismicity in the region of the 1885 earthquake, possibly delineating an onshore seismic zone separate from the sparse seismicity along the continental shelf. This large midplate earthquake will likely affect future reevaluations of seismic hazard in midplate South America.

GROUND MOTION PREDICTION AT THE DAM SITES IN SW ROMANIA FOR MODERATE VRANCEA SUBCRUSTAL EARTHQUAKES

The seismic hazard studies of the last 30 years have been largely carried out taking into account the needs of the construction engineers, by linking the specific quantities of soil movement with the physical parameters determined instrumentally, namely, with the maximum values of soil acceleration. At present, interest in the results of hazard studies has increased and has extended to other areas such as insurance or design companies, environmental protection, etc. A fundamental element in the estimation of seismic hazard is the variation of the amplitude of the movement of the soil according to the distance, magnitude and local conditions. To understand and prevent the effects of the strong Vrancea earthquakes in the dam sites located in the South West of Romania, we study the seismic waves attenuation relations using the accelerations recorded by the national network of K2 accelerometers, following the moderate Vrancea intermediate earthquakes. The study area includes the largest agglomeration of dams in Romania, with almost 100 dams out of the 250 large dams. One of the most important specific requirements towards dams' safety is the seismic risk and hazard assessment and the computation of attenuation relationships is one of the most important steps of the work. The main objective of the present work is the evaluation of the specific attenuation relationships of the seismic wave propagating from Vrancea subcrustal focus toward south-west, with direct application for the dams situated in the area.