Plastic Hinge Length for Lightly Reinforced Rectangular Concrete Walls

This research investigates the plastic hinge length in lightly reinforced rectangular walls typically found in regions of low-to-moderate seismicity. Poor performance has been exhibited by lightly reinforced concrete walls in past earthquake events. A series of finite element analyses have been carried out which demonstrate that if the longitudinal reinforcement ratio in the wall is below a certain threshold value, there will not be sufficient reinforcement to cause secondary cracking, and instead fracture of the longitudinal reinforcement at a single crack could occur. A plastic hinge length equation has been derived based on the results from the numerical simulations.     

Archeoseismicity and environmental crises at the Sialk Mounds,Central Iranian Plateau,since the Early Neolithic

During the long-lasting cultural sequences of the Shurābeh and Sialk archeological mounds (6200–550 BC) the inhabitants encountered numerous diversified crises along a narrow fertile passageway at the edge of the Central Iranian Plateau Great Desert. Some of the threats may be attributed to earthquakes, drastic climatic changes, and man-made environmental deterioration, which possibly led to the settlement withdrawing at different stages toward a more suitable location. Our study identified the occurrence of a large-magnitude earthquake around 3800 BC along the Kāshān fault, which is well-documented by various lines of circumstantial evidence, including: (i) numerous contemporaneous smashed skeletons and artifacts underneath collapsed walls and ceiling debris in several different areas; (ii) tilted and collapsed walls; (iii) nearly N–S oriented fallen large storage jars; and (iv) nearly vertical deep ground fractures cutting walls and floors of the Sialk III₅ South Mound settlement. Archeological data also shows additional stratigraphic discontinuities and damages that may be attributed to earthquakes. However, damage features in limited exposed trenches are less conclusive and require additional careful excavations. Apparent ancient paleo-architectural innovative attempts to enhance the coherency/elasticity of the structures and minimize earthquake damage to buildings were also noted, suggesting the indigenous earthquake hazard mitigation endeavor. There seems to be a correlation between some site abandonment dates and possible drastic regional draught/cooling events. The natural and anthropogenic impacts addressed in this study constituted major threats to the sensitive archeological settlements at the fringe of the desert and the vicinity of the Kāshān active fault since antiquity.     

The 1561 Earthquake(s) in Southern Italy: New Insights into a Complex Seismic Sequence

In the summer of 1561, a strong seismic sequence struck southern Italy, then the Spanish-ruled Kingdom of Naples. Both the Italian seismological tradition and the latest catalogues locate it in the Vallo di Diano (Diano Valley), a low-seismicity intermontane basin 100 km south-east of Naples. We explore the hypothesis that current perception of the 1561 earthquake is distorted by the nature of the historical dataset from which its parameters have been assessed, and which mostly derive from a single—albeit very detailed—primary source. We present and discuss several previously unconsidered original accounts. Our results cast doubts on the traditional interpretation of the earthquake, which could have been either one Vallo di Diano mainshock or several strong earthquakes within a time/space window compact enough for contemporary viewers to perceive them as one. Unquestionably, there is much more to the 1561 earthquake(s) than previously appeared. We hope that this groundbreaking effort will rekindle the interest of the seismological community in this seismic episode, our knowledge of which is still far from complete.     

The Mw 6.4 SW-Achaia (Western Greece) Earthquake of 8 June 2008: Seismological,Field, GPS Observations,and Stress Modeling

On June 8, 2008 a Mw = 6.4 earthquake occurred in NW Peloponnese, western Greece. This event is the largest strike-slip earthquake to occur in western Greece during the past 25 years. No surface rupture was observed. Many rock falls, slides, and liquefaction features have been found as is typical for an earthquake of this size. Double-difference relocations of 370 aftershocks show a linear pattern of events and define a clear NE-SW striking mainshock fault plane. The hypocentrer was determined at 18 km depth beneath village Mihoi in SW Achaia. The 24-hr aftershock region extends approximately 30 km in length, and the width of the surface projection of the aftershocks ranges between 5–10 km. The depth of the aftershocks rarely exceeds 22 km. Analysis of high-rate GPS data showed that station RLS (Riolos) which is located 12.8 km N5°W of the epicenter was displaced co-seismically 7 mm to the North in agreement with right-lateral kinematics of the rupture. Static (Coulomb) stress transfer analysis indicates loading of faults near the towns of Patras (north) and Amaliada (south), respectively. The earthquake put more emphasis on the role of strike-slip in the deformation of western Greece also indicating that seismic strain is partitioned between strike-slip and normal-slip events due to obliquity of the Nubia (Africa) – Eurasia convergence.     

Seismic Hazard Assessment of the NW Himalayan Fold-and-Thrust Belt,Pakistan, Using Probabilistic Approach

The Seismic Hazard Assessment (SHA) based on probabilistic approach has been carried out for the entire seismically active NW Himalayan Fold and Thrust Belt in Pakistan. Additional information in the form of earthquake catalog, delineation of 41 active faults in a structural map, their relationship to the seismicity, and establishment of seismotectonic zones has also been undertaken.

From the distribution of the 813 events within the study area, it appears that seismicity (≥4.0 M_w) is associated with both surface and blind faults. The clustering of events in specific parts along the surface faults shows that some fault segments, especially in the hinterland zone, are more active. In parts of the active deformational front, like the Salt Range, southern Potwar and Bannu, lesser seismic activity (≥4.0 M_w) could be due to damping effect of the thick Precambrian salt.

A majority of the earthquakes (86%) range in magnitude from 4.0 to 4.9 M_w, followed by 107 events (13%) ranging from 5.0 to 5.9 M_w. The remaining 1% range from 6.0 to 6.7 M_w. There is a predominance of shallow seismicity (<50 km focal depth). Larger magnitudes events are more in the hinterland zone. In contrast, based on distribution of 683 (≥4.0 M_w) events, a deeper level of seismicity (50 to 200 km) prevails especially in the adjoining Hindukush Range of Afghanistan.

Four seismotectonic zones have been established in the area. The b value is highest for the Peshawar-Hazara Seismic Zone (PHSZ) at 1.27, followed by 1.12 for the Surghar-Kurram Seismic Zone (SKSZ). The Swat-Astor Seismic Zone (SASZ) and Kohat-Potwar-Salt Range Seismic Zone (KPSZ) have b values of 0.99 and 1.03, respectively, thereby indicating the occurrence of more events of relatively higher magnitude as compared to the other two zones. The mean activity rate of the earthquakes (λ) ranges from 4.26 to 1.73. In decreasing order, the values are 4.26, 2.62, 2.07, and 1.73 for PHSZ, SASZ, KPSZ, and SKSZ, respectively. Using four regression relationships, the maximum potential magnitude (m₁) has been determined for the 4 Quaternary faults. The highest value within each seismic zone represents its m₁. Our calculations show that m₁ is 7.8 in the hinterland (SASZ and PHSZ) and 7.4 in the foreland part (KPSZ and SKSZ).

SHA, incorporating probabilistic approach, has been undertaken at 10 sites, along with disaggregation at the assigned amplitude of 0.2g. Pakistan does not have an attenuation equation of its own. The two equations of Ambraseys et al. (1996) Ambraseys, N. N., Simpson, K. A. and Bommer, J. J. 1996. Prediction of horizontal response spectra in Europe. Earthquake Engineering and Structural Dynamics, 25: 371–400. [Crossref], [Web of Science ®] , [Google Scholar] and Boore et al. (1997) Boore, D. M., Joyner, W. B. and Fumal, T. E. 1997. Equations from estimating horizontal response spectra and peak acceleration from western North American earthquakes: a summary of recent work. Seismological Research Letters, 68: 128–153. [Crossref] , [Google Scholar] have been used and the results obtained using the equation of Boore et al. (1997) Boore, D. M., Joyner, W. B. and Fumal, T. E. 1997. Equations from estimating horizontal response spectra and peak acceleration from western North American earthquakes: a summary of recent work. Seismological Research Letters, 68: 128–153. [Crossref] , [Google Scholar] have been preferred. In the Probabilistic seismic hazard assessment (PSHA), the PGA values with 10% probability of exceedance in the 50 years, i.e., the return period of 475, have been determined using the EZ-FRISK (6.2 beta version) software. Best-estimated seismic hazard parameters (λ, m₁, m₀, and the β value) of the four seismic zones were used as the input. Results were generated in the form of total hazard curves. Values obtained range from 0.08g (for Bannu) to 0.21g (for Malakand and Kohat). For the other seven sites they are: Astore (0.082g), Kaghan (0.12g), Muzaffarabad (0.13g), Islamabad and Peshawar (0.15g), Talagang (0.16g), and Mangla (0.18g). High population density and more poorly constructed structures in Rawalpindi (twin city of Islamabad) and Peshawar make them more hazardous.     

Tsunamigenic Analysis in and around Makran

The Makran region is only segment east of the Mediterranean and west of Andaman arc in which subduction of oceanic lithosphere is still an ongoing process. We applied statistical models for the possible explanation of earthquakes in and around Makran, and described a method of Fault Plane Solutions to present seismicity picture in the investigated region, and their possible tsunamigenic effects on Gwadar Coast. We also applied the Community Modeling Interface for Tsunami (ComMIT) for the estimation of tsunami hazard along the coast of Gwader due to the Arabian and Eurasian plate boundary earthquakes along the Makran subduction zone.