THE GPR MEASUREMENTS ON HAGIA SOPHIA'S SURFACES FACING THE NAOS

Abstract

~~Hagia Sophia (Hagia Sophi? / ?γ?a Σoϕ?a), which is currently used as a Museum, was first constructed as an Orthodox Church between AD 532-537 by the Byzantine Emperor I. Justinianos. Later, during the rule of the Latin Empire, it was used as a Catholic Church for a short period of time. After the conquest of Istanbul (Constantinople) by the Turks in 1453, the Ottoman Sultan Mehmed the Conqueror (Mehmed II) turned the church into to a mosque. Hagia Sophia, the oldest Cathedral in the world, had retained the title of being the biggest cathedral in the world for approximately thousand years since its construction. It was the patriarchal church of the Constantinople Patriarchate and the center of Eastern Orthodox Church. Currently, Hagia Sophia holds the fourth place in terms of surface area. This structure, which combines basilica plan and central plan, is a basilica with a dome; and thus, it constitutes a milestone in the history of architecture with its dome transition and load-bearing system. It was constructed by famous architects of the 6th century, Isidore of Miletus and Anthemius of Tralles. The current building of Hagia Sophia is known as the Third Hagia Sophia, because, in fact, it is the third church built on the same spot. The first two churches were demolished during uprisings. Hagia Sophia’s central dome, the largest dome of the period, collapsed for a several times during the Byzantine period. However, after Mimar Sinan had added retaining walls, it never collapsed again. In the 553 and 557 earthquakes, after a short period of its construction, fractures developed in the central dome as well as in the eastern semi-dome. In the earthquake on May 7th, 558 the main dome collapsed completely and the first ambon, ciborium and altar were smashed and destroyed. Taking a lesson from this earthquake, in order to evade another collapse, this time light material was used in the construction of the dome and the dome was built 6.25 meters higher than its previous height. The fire in 859, the earthquake in 869 resulting in the collapse of its semi-dome and the 989 earthquake causing damage in its central dome may be listed among the consequent depravations that Hagia Sophia went through. Damage or plunder of Hagia Sophia by the people was first brought about by the Crusades under the command of Dandalo, reign of Venice Republic during the Fourth Crusades. In 1261, four supporting components in the west of Hagia Sophia were built. In 1317, other supporting components were added in the northern and eastern sections of Hagia Sophia as well. In the 1344 earthquake, new fractures appeared in the dome and some parts of the building collapsed on May 19th, 1346. After this incident, restoration works were initiated in 1354. Until today, many restoration works have been led in Hagia Sophia. The first significant restoration took place after the 558 earthquake and lasted until 562. Later, after the earthquake in 989, some parts of the dome and the left arch were repaired. After 6 years of repair work, Hagia Sophia was re-opened for worship in 994. The third and the most important restoration was made by Mimar Sinan’s adding retaining walls. Analyzed in terms of architecture, Hagia Sophia is constituted of a central area called naos, two side naves in north and south, an apsis located in the eastern end and inner and outer narthexes with doors located in the western side. GPR measurements were conducted on the surfaces of four columns (pillars) facing the naos (inner space, central hall) and pendentives transitory to the columns and facing the naos. In the GPR measurements, by using 1200 and 500 MHz shielded antennas, scanning was made along transverse and longitudinal profiles from the base to the dome. Obtained radargrams were displayed in two (2D) and three dimensional (3D) forms. Floor maps were created to be able to better trace high amplitude anomalies, to identify structural deformations and to trace horizontal changes at different levels from surfaces to the inner wall. Locations where surface lining with marble content de-links from the mortar, deterioration in the marble and deformations on the walls behind the linings were identified as initial findings. A significant congruence was found between results of 3 Dimensional scanning, conducted by the 3D Laser Scanner, and the GPR measurements made to identify visible deformations on the walls. Findings obtained in this research will make a significant contribution in developing restoration projects.