MMI Scale Research Articles

ASSESSMENT OF GEOTECHNICAL SEISMIC HAZARD OF THE DHAMAR CITY, YEMEN

The objective of this paper is to asses s and present the geotechnical seismic hazard in the Dhmarar city, Yemen. During the present study assessment for the geotechnical seismic hazard was carried out in an area of 100 km radius around Dhamar city. Based on the Geotechnical data obtained for th is study, Seismotectonic maps are constructed showing the major lineaments to trend in NW - SE, NE - SW and SWW - NEE directions that attribute to the general directions of the axial of the Red Sea and the Gulf of Aden. The earthquake catalogue of the region fac ilitated the classification of seismicity of the region into three major seismic periods. The b value is classified as low and is the characteristic of the continental rift zone that corroborates well with the geological evolution of the study area. Isointensity zoning and PGA maps with two epicentral distances of zero and 50 km were constructed. Th e Isointensity maps indicated that the intensity of the entire study region ranges from II to VIII on MMI scale. Micro level study carried out in the immediate vicinity of Dhamar city indicates the region to be slightly hazardous whose intensity ranges fro m II to III on MMI scale. The PGA values for the region and the area under investigation vary from zero to 500 and 20 to 180 cm/sec 2 respectively. Based on the geotechnical field evidences and statistical data, the relation between seismicity, volcanicity and thermal springs are strong.

Seismic Behaviour of Single - Story URM Buildings with Light Weight Steel Roof

Single story masonry buildings with light weight steel roof were designed and constructed on a specially designed shaking table at the Spoornet Laboratory in Johannesburg. The test structures were instrumented with LVDTs and accelerometers to measure the structural responses and behaviours of the structures at the bottom, middle and top of the in-plane and the out-of-plane walls. Accelerometers were also mounted on top of the steel roof to measure the roof responses. Displacements of the structures relative to the shaking table was measured from a rigid octagonal reference frame located inside the structure. The responses of two types of structures are reported. The first is a conventional block masonry structure. The second test was carried out on dry-stack interlocking block masonry structure which relies mainly on the interlocking features for structural resistance. The conventional masonry structure was subjected to 52 test runs ranging from minor peak ground acceleration (PGA = 0.05 g) to severe (PGA = 0.7 g). A similar test pattern was also used for loading the dry-stack system until failure was attained. Results obtained from the conventional structure show that test runs 1-10 caused no visible damage. Test run 11 produced cracks along the base of the in-plane wall due to racking, and surface or hairline cracks on the plastered surface of out-of-plane walls. Vertical cracks above the lintel level of the inplane wall was noticed after the test run 19. The progress of the above cracks was seen more clearly during the subsequent test runs. During test run 33 an inclined shear crack was developed. Widening of this shear crack was seen during subsequent tests leading ultimately to the collapse of parts of the walls during test run 52 and the test was concluded. The PGA at last run for the conventional masonry structure was 0.7 g which is equivalent to a magnitude of between 7.4 and 8.1 on the Richter scale or XI on the Modified Mercalli Intensity, MMI scale. This paper reports the structural responses of the test structures to simulated earthquake loading.

Intensity and isoseismal map of 25th November 2007 Delhi earthquake

An earthquake of magnitude ML: 4.3 occurred on 25th November 2007 (2312 UTC) in Delhi with hypocenter at 28.56° N / 77.08° E and focal depth 33.1 km. The epicenter was at about 21 km SW of Delhi University. It was widely felt in and around Delhi and created panic among the local populace. A macroseismic survey was conducted in about ten days starting from 27th November, 2007 at 89 locations covering an area of about 1500 sq. km in Delhi and its neighborhood through a questionnaire. The results of the macroseismic survey allowed establishment of spatial distribution of the earthquake effects in the form of isoseismal map generated using geo-statistical analysis tool of ArcGIS 9.1. The isoseismal map shows that most parts of Delhi region experienced an intensity of V on MMI scale, except on northern most region of Delhi where intensity was found IV. The mean isoseismal radii for the zones V, IV, III and II are 29.13, 57.78, 83.63 and 100.75 km, respectively. The orientation of elongated epicentral track of intensity field shows that the stress release was pronounced along Delhi-Sargodha ridge and earthquake was attributed to activities of this ridge.

Validation of a kinematic and parametric approach to calculating intensity scenarios

We employ our semi-empirical kinematic model for shear body waves ( KF) [Sirovich L. A simple algorithm for tracing out synthetic isoseismals. Bull Seism Soc Am 1996;86(4):1019–27; Sirovich L. Synthetic isoseismals of three earthquakes in California-Nevada. Soil Dyn Earthquake Eng 1997;16:353–62] to back-predict and then validate the regional intensity scenario of a destructive earthquake (Loma Prieta, California, M s 7.1, October 17, 1989). Only the pre-1988 geological and seismotectonic knowledge was used to set the 11 source parameters of KF (in this sense, our procedure was deterministic). Then, the ranges of the pre-1988 uncertainties were explored by grid search and the parametric combination produced 59,049 sources. The quality of our prediction was measured using the field intensities of 1989 by the US Geological Survey (in the MMI scale). The squared scenario residuals are: 73 for the mean KF scenario and 123 for the best available empirical attenuation of MMI intensity. We stress that, before using KF in the forward mode, its automatic inverse application has already been validated by refinding a series of earthquake sources [Gentile F, Pettenati F, Sirovich L. Validation of the automatic nonlinear source inversion of the US geological survey intensities of the Whittier Narrows, 1987 Earthquake. Bull Seism Soc Am 2004;94(5):1737–47; Pettenati F, Sirovich L. Intensity-based source inversion of three destructive California earthquakes. Bull Seism Soc Am 2007;97(5):1587–606; Sirovich L, Pettenati F. Source inversion of intensity patterns of earthquakes: a destructive shock in 1936 in northeast Italy. J Geophys Res 2004;109:B10309, doi:10.1029/2003JB002919:1–16]. If our technique had been available at the time, the 1989 pattern of damage south of San Francisco would have been conservatively foreseen even from 1983 on.

Recent seismic activity in the NW Himalayan Fold and Thrust Belt, Pakistan: focal mechanism solution and its tectonic implications

Abstract The Himalayas in northern Pakistan have been the site of several disastrous earthquakes of moderate to high intensity. The 8 October 2005 Muzaffarabad earthquake, with magnitude M w 7.6, occurred in the NW Himalayan Fold and Thrust Belt at 08:50:38 local time. The epicentre of the main shock was located 19 km NE of Muzaffarabad. This earthquake took a death toll of more than 80 000 human lives and caused widespread destruction in Kashmir and north Pakistan, particularly in the towns of Muzaffarabad, Bagh, Rawalakot, Mansehra, Balakot, Abbottabad and Batgram. Based on the information obtained from print and electronic media (and for some areas from field studies), an intensity of X (MMI scale) has been assigned at the epicentral location including the localities of Muzaffarabad and Balakot. Epicentral distribution of 300 aftershocks indicates that more than one tectonic subdivision of the fold belt have experienced instability. Focal depths indicate that most activity is confined to a narrow depth range (5–20 km). Further extension of the Indus Kohistan Seismic Zone in the Hazara–Kashmir syntaxial area and activation of more than one fault seem to be the cause of this seismic activity, as suggested by the focal mechanism of the main event and depth distribution of the aftershocks. About 100 large landslides caused by active faulting have been observed in the rupture zones near Balakot, Muzaffarabad, Kardalla, Hattian Bala, Sarain, Sunddangali and Bagh, through field studies and satellite images.

Seismic Intensity Estimation through Questionnaire Survey and Collapse Rates of Various Building Types in the 2003 Bam, Iran, Earthquake

Seismic intensity in the epicentral area of the 2003 Bam, Iran earthquake is estimated using a questionnaire survey conducted two months after the earthquake. The estimated average seismic intensity on the Japan Meteorological Agency (JMA) scale is 6.1 (VIII to IX in the MMI scale). The peak frequency of the horizontal-to-vertical spectral ratio derived from microtremor measurements conducted during reconnaissance is also compared with the seismic intensity. Collapse rates for various structure types, such as adobe, unreinforced/reinforced masonry, steel-frame, and reinforced concrete, are obtained by counting the number of demolished buildings within an area of about 50-m radius around an observation point. Results show large differences in collapse rates between unreinforced and reinforced masonry, and suggest the upper limit of seismic intensity that unreinforced masonry can sustain. This fact can be utilized for an initial damage assessment within affected areas after large earthquakes.

Magnitude Recurrence Relations for Colorado Earthquakes

Colorado has a significant potential for damaging earthquakes. The Colorado Geological Survey has identified 92 potentially active faults. Two faults have documented slip-rates approaching 1 mm per year. Four hundred and seventy-seven Colorado earthquakes have been felt and/or equaled or exceeded magnitude of 2.0 between 1870 and 1996. Eighty-two earthquakes have equaled or exceeded an MMI Scale of V. Colorado's largest historical earthquake, which occurred on 7 November 1882 (8 November UCT), had an estimated magnitude of 6.5 and maximum MMI of VII to VIII. Colorado's maximum credible earthquake has been estimated at 7.5 ML. In this paper we analyze independent earthquakes (foreshocks, aftershocks, and fluid-injection induced earthquakes removed) to develop magnitude-recurrence relations. Analysis of instrumentally measured earthquakes predicts that a 6.5 ML or larger earthquake occurring somewhere in Colorado has a mean recurrence interval of about 420 years. A magnitude 6.6 ML earthquake has a 10 percent Poisson's probability of exceedance in 50 years. A 7.5 ML earthquake has a 2 percent Poisson's probability of exceedance in 50 years. Colorado's magnitude-recurrence (Gutenberg-Richter) relation is log N=2.58−0.80 ML.

Seismic Intensity and Fourier Acceleration Spectra: Revised Relationship

This paper presents a revised method for estimating the seismic intensity (MMI or MSK scale) using Fourier amplitude spectra (FAS) of ground acceleration. The improvement of the recently proposed technique (Sokolov and Chernov 1998) has been made on the basis of the data, which were obtained recently during strong earthquakes that occurred throughout the world. The total amount of the used data (horizontal components of ground-motion recordings) is about 1,150 records, while the database of 300 recordings was used in the previous study. The method implies that the seismic intensity is determined by the level of ground motion spectral amplitudes in the frequency range of 0.4–13 Hz. The corresponding empirical relationships between FAS and each intensity level were developed. The method is validated by comparison of the results of the technique application with the empirical data, which have not been included in the database. The Romanian earthquakes (intermediate-depth events of 1977, 1986, and 1990) and the recent 1999 Hector Mine earthquake in southern California were used for this purpose. In general, the FAS intensity shows a good agreement with the reported intensity, and the average residuals do not exceed ±0.3 intensity units and standard deviation is about 0.4-0.6. Evaluation of seismic intensity distribution using region- and site-dependent spectral models, as well as calculation of instrumental intensity map for the recent 1999 Chi-Chi earthquake, Taiwan, show that the FAS intensity clearly reflects the regional (source scaling and attenuation relation) and local (soil response) peculiarities of ground motion.

Modelling of rupture planes for peak ground accelerations and its application to the isoseismal map of MMI scale in Indian region

The rupture plane for an earthquake has been modelledby using the semi empirical technique of Midorikawa(1993). This technique estimates ground accelerationby modelling the rupture process during an earthquake.Modifications in this technique have been made for itsapplication to the Indian region. This has been tested forthe Uttarkashi earthquake of 20th Oct, 1991, India, whichwas well recorded at thirteen stations of installedstrong motion array in this region. After testingseveral possible rupture models, a final model has beenselected and peak ground acceleration due to thismodel is simulated at thirteen different stations.Dependency of methodology on model parameters, e.g.dip and mode of rupture propagation have also beenstudied in detail.Using this technique synthetic isoseismal maps wereprepared by converting peak ground acceleration intoMMI scale. Dependency of rupture models on syntheticisoseismals has also been studied in detail. Usingthis method, peak ground acceleration for the Laturearthquake of Sept 30, 1993 has been obtained atvarious places within meisoseismal area. Synthetic andfield intensity was compared at various well-knownsites. Since the region was not covered by anyinstrumental array during Latur earthquake, thesimulated peak ground accelerations are expected toserve basis of design criteria in this region.

Correlation of seismic intensity with Fourier acceleration spectra

We present a method for estimating the seismic intensity in terms of MMI or MSK scale using Fourier amplitude spectra of ground acceleration. The method implies that severity of earthquake ground motion is determined by spectral amplitudes in relatively narrow frequency band: so-called “representative frequencies”, at decreasing frequencies (from 7–8 Hz for small intensities to 0.7 – 1.0 Hz for MMI(MSK) = VIII–IX) with increasing intensity level. It is examined through estimation of probable intensity at a site using recordings of recent earthquakes in several seismic regions and prediction of intensity distribution patterns for some earthquakes. Seismic hazard maps, in terms of intensity levels based upon the proposed approach, should describe regional features of seismic waves excitation and propagation, as well as local ground conditions.

On the Correlation of Seismic Intensity with Fourier Amplitude Spectra

This paper presents a method for estimating the seismic intensity (MMI or MSK scale) using Fourier amplitude spectra of ground acceleration. The method implies that the severity of earthquake ground motion is determined by spectral amplitudes in a relatively narrow frequency band: so-called “representative frequencies”, at decreasing frequencies (from 7-8 Hz for small intensities to 0.7-1.0 Hz for MMI=VIII-IX) with increasing intensity level. It is examined through estimation of probable intensity at a site using recordings of recent earthquakes in several seismic regions, and prediction of intensity distribution patterns for the Coalinga, California earthquake of May 2, 1983, and the Spitak, Armenia earthquake of December 7, 1988. Seismic hazard maps, in terms of intensity levels based upon the proposed approach, should describe regional features of seismic waves excitation and propagation, as well as local ground conditions.