Integration of global positioning system (GPS) and inertial navigation system (INS) is used in airborne gravimetry to gravity field recovery. Since GPS computed position is noisy therefore the GPS ACCELERATION which is the result of twice differentiation of GPS position will be too noisy as well. In this paper IIR low-pass filter and Kalman filter are used to smoothing the GPS ACCELERATION and their result compared to B-spline smoother result. B-spline smoothing accuracy is reported about 1mGal in this paper data, therefore B-spline smoothing considered as a reference smoothing method. The correlation of IIR low-pass filter and Kalman filter results with B-spline smoothing result is about 97.55 and 99.83 percent, respectively. It shows that the Kalman filter result is closer to B-spline smoother. On the other hand, along with ease of design of IIR lowpass filter some other advantages such as fast computing algorithm in signal processing unlimited response hit and less memory requirement are worth mentioning. Therefore, in project with huge among of data the IIR low-pass filter could be efficient and causes the time and cost saving. Mentioned smoothing methods can also be used in INS instrumental noise reduction. Therefore, less accurate INS can be used in integration with GPS, which causes the INS cost saving and project productivity promotion.

This paper suggests modified proportional navigation (PN) with a weighted combination of linear ACCELERATION and line-of-sight (LOS) ACCELERATION feedback. For this purpose, a comprehensive miss distance analysis is carried out for PN with linear ACCELERATION feedback and PN with LOS ACCELERATION feedback using a fifth-order binomial guidance and control system. The miss distance (MD) due to initial heading error, target ACCELERATION, and seeker noise are separately analyzed. A modified PN with ACCELERATION feedback using variable gains is suggested based on MD analysis for infrared seekers as a special case. The PN strategies are compared using an equivalent effective navigation ratio, defined using the LOS rate profile solution. In addition, the first-order optimal guidance law is converted into PN with PD block with variable gains.

Full Text [PDF 1187KB] The region of northwestern Iran is exceptional within the Arabian-Eurasian continental collision zone. The tectonics is dominated by the NW-SE striking right-lateral North Tabriz Fault (NTF) and regional seismicity (historical and modern one) concentrates. The NTF is a major seismogenic fault in NW Iran. The last damaging earthquakes on this fault occurred in 1721, rupturing the southeastern fault segment, and in 1780, rupturing the northwestern one. The understanding of the seismic behavior of this fault is critical for assessing the hazard in Tabriz, one of the major cities of Iran; the city suffered major damage in both the 1721 and 1780 events. The north of the NTF seismicity is rare, and almost nothing has been revealed about activity of the structures until now.On 11th of August 2012, the region was surprisingly struck by a shallow Mw 6.5 earthquake with a pure right-lateral strike-slip character only about 50 km to the north of the NTF. An east-west striking surface rupture of about 20 km length was observed in the field by Geological Survey of Iran. Only 11 minutes later and about 6 km further to NW, a second shallow event with Mw 6.2 occurred. It showed an NE-SW oriented oblique thrust mechanism. This earthquake sequence provided an opportunity to understand better the processes of active deformations and their causes in NW Iran.Ground-motion relations describing the expected amplitudes of this motion as functions of the magnitude and distance are key components of seismic hazard analyses. Ground-motion (attenuation) relations are used to estimate strong ground motion for many engineering and seismological applications. Where strong motion recordings are abundant, these relations are developed empirically from strong-motion recordings. Where recordings are limited, they are often developed from seismological models using stochastic and theoretical methods.The stochastic model is a widely-used tool to simulate ACCELERATION time series and develop ground motion relations (Hanks and McGuire, 1981; Boore, 1983; Boore and Atkinson, 1987; Atkinson and Boore, 1995 and 1997; Atkinson and Silva, 1997 and 2000). The stochastic method begins with the specification of the Fourier spectrum of the ground motion as a function of magnitude and distance. The ACCELERATION spectrum is modeled by a spectrum with ω2 shape, where ω is the angular frequency (Aki, 1967; Brune, 1970; Boore 1983). Finite fault modeling has been an important tool for the prediction of ground motion near the epicenters of large earthquakes (Hartzel, 1978; Irikura, 1983; Joyner and Boore, 1986; Heaton and Hartzel, 1986; Somerville et al., 1991; Tumarkin and Archuleta, 1994; Zeng et al., 1994; Beresnev and Atkinson, 1998a). One of the most useful methods to simulate ground motion for a large earthquake is based on the simulation of some small earthquakes as subfaults that comprise a big fault. A large fault is divided into N subfaults, and each subfault is considered as a small point source (introduced by Hartzel, 1978).In this study, the first region-specific ground motion relations were developed for seismic hazard analysis of NW Iran. The attenuation relation for the horizontal ACCELERATION response spectrum in a period of 0-4 s, with a magnitude range of Mw=5 to 7.7 and distances up to 150 km were established. We used 51 waveforms recorded on a rock site in the NW Iran. Due to the paucity of the data at small distances and large magnitudes, we applied the stochastic method to simulate waveforms for different magnitudes and distances. To overcome the incompleteness of the data set, we simulated 1240 ACCELERATION time series for magnitudes from M5.0 to M7.7 and magnitude steps of 0.2 units for the North Tabriz fault and M5.0 to 6.7 and magnitude steps of 0.5 units for the Ahar fault. The relations were derived by a maximum likelihood regression algorithm from Joyner and Boore (1993) on a set of 1240 simulated strong-motion records and 51 observed ground motions recorded on the rock site in this region. The theoretical-empirical ground motion relation for NW Iran was compared to the ground motion relations for the other regions and had a good agreement with them especially with Akkar and Bommer relations for Europe, the Mediterranean Region and the Middle East. The present results will be useful in estimating strong ground motion parameters and in the earthquake resistant designs in this region.

Empirical ground motion models for the average horizontal component of peak ground motion and ACCELERATION response spectra from shallow crustal earthquakes are derived using near-source database. These models were derived using a worldwide dataset consisted of corrected and processed accelerograms of 646 strong-motion records recorded with 60 (km) of the surface projection of earthquakes between Mw 5.2 and 7.8. Model is function of earthquake mechanism, distance from source to site, local average shear wave velocity, nonlinear soil response, sediment depth, depth-to-top of rupture, hanging wall effects and faulting mechanism. Non-linear site effects are constrained by equivalent linear models. An important additional source parameter, depth to the top is also included. The hanging wall effect is included with an improved model that varies smoothly as a function of the source properties, such as magnitude, dip, distance, depth, and the site location.

The Endurance Time (ET) method is a time-history based dynamic pushover procedure. In this method, the structures are subjected to gradually intensifying ACCELERATION called an ACCELERATION function. Then, their performances are assessed from linear to collapse level based on the interval time through which they can satisfy the required objectives. ET ACCELERATION Functions (ETAFs) are calibrated upon actual earthquake spectra compatible with the Iranian National Building Code (standard no. 2800). In this code, there is no distinction between far and near fault regions. ETAFs scale based spectrum increases uniformly at all periods as the time passes which is why this uniform increment is not desirable in near fault earthquakes. As the rupture propagation is oriented towards a site, near fault earthquakes have further spectral ACCELERATION in the period over 0.6 sec compared to far fault earthquakes. The shape of the spectrum becomes richer over long periods as its level increases. In this research, ETAFs are presented for near fault target spectra, provided by Abrahamson-Silva attenuation relations. These relations have been modified by Somerville near fault correction coefficients. According to the results obtained in this research, while the new ACCELERATION function can model directivity effects at higher periods, it also satisfies endurance time concepts.