Protecting culturally significant buildings II

July 11

Guralp equipment has again been used to monitor the response to seismic shaking and the structural health of an important, culturally significant building. Several years ago, the Fatih Sultan Mehmet Mosque in Istanbul was equipped for that purpose with several 5TD accelerometers (more details…). Now, a similar network has been installed in the Lala Mustafa Paşa Mosque in the city of Famagusta in North Cyprus.

The West facade of the Lala Paşa Mosque

Building of the Lala Mustafa Paşa Mosque started in 1298 under the French Lusignan dynasty and it was consecrated in 1328 as the Saint Nicolas Cathedral. The two towers of the Western facade were damaged by earthquakes and, in 1571, suffered further damage when the Ottomans seized Cyprus. The new rulers renamed the cathedral the Ayasofya (Saint Sophia) Mosque of Gazimagosa and added a new minaret. All human images, whether carved, painted or set in glass, were removed or plastered over but the damage to the towers was not repaired. In 1954, the name was changed again to the Lala Mustafa Paşa Mosque, in honour of the commander of the 1570 Ottoman conquest. Although French Gothic architecture is not unusual in Cyprus, the mosque is the largest medieval building in Famagusta and is still in active use as a place of worship, as well as being a popular tourist destination.

Sentez Earth and Structure Engineering Ltd – Guralp Systems Ltd’s distributor and technical service center for Turkey and beyond – won the contract for monitoring the building under an E.U. project. For that purpose, Sentez engineers set up on-line strong-motion instrumentation at several key locations in the building to record the response of the structure to ground movements and identify areas which may be susceptible to damage. This turn-key project included site selection, installation, commissioning and the training of monitoring personnel.

CMG-5TDE top view

The network comprised 10 5TDE triaxial digital accelerometers linked by cable and WiFi to a PC running Scream, Guralp Systems Ltd’s configuration, real-time acquisition and monitoring software.

The 5TDE is a fully digital, triaxial, force-feedback accelerometer with a large dynamic range, suitable for seismology, hazard mitigation and civil engineering applications. An on-board, Linux-based acquisition module offers remote monitoring and control, with unparalleled flexibility. The 5TDE combines the well-regarded 5T strong motion instrument, an integrated DM24 digitizer and an EAM embedded acquisition module to form a low noise sensor with on-board and external storage options, a convenient web-based user interface and multi-protocol communications over serial and Ethernet connections.

CMG-5TDE angled view

5TDE Key features:

  • Low-noise components for high precision and extra dynamic range
  • Full-scale sensitivity from 0.1 to 4.0 g
  • Low pass corner from 50 to 100 Hz
  • No mass-locking or sensor levelling required
  • Isolated power supply for 10 – 36 V operation
  • Robust and waterproof
  • Up to 256 GB of on-board Flash memory storage
  • Unlimited external USB mass storage
  • Data recording in GCF or miniSEED formats
  • Fast data download over Ethernet or USB
  • Configuration via serial or Ethernet: command-line or web-based
  • Full network security suite, including HTTPS and firewall, allows direct, permanent connection to the Internet.
  • Optional USB Flash memory stick storage option
  • LCD display allows operators to monitor triggers and memory usage in real time
  • Powerful, flexible Linux operating system

The Sentez team used specially isolated housings to cover the instruments located outside the building, to protect them against heat and rain.

External instrument enclosure with GPS receiver mounted on roof ridge

Instrument mounted on external wall

Control and monitoring room

Each instrument within the network was linked via a 16-port Ethernet switch. The network is powered from a central room which provides a constant power and TCP/IP connection for data streams to reach a central PC running Scream. An ADSL modem using NAT provides Internet access for the network equipment and forwards requests for GCF data from the Scream-Server.

Physical locations of the instruments on and around the mosque Logical locations of the instruments

The large internal flash memory of 5TDE (16 Gb) provides a unique data storage capability in the event of any network problems but, in normal use, the real-time data are stored on the Scream PC in the control room and also forwarded to a remote server for tertiary storage.

With this setup, small earthquakes can be detected at the ground floor of the building and compared with the motion of the sensors on higher levels. Differences between the traces are being analysed to provide information about the vibrational modes of the building. This information is used to decide which sections of the mosque are in need of strengthening in order to prevent significant damage during larger earthquakes.

View of instruments deployed along the north wall

Minaret photo courtesy of Daniel Attarian.