Eman Al Khatibi1, Kamal Abou Elenean1

DUBAI SEISMIC NETWORK (DSN)

1 Dubai Municipality, Survey Department, P.O. Box: 67 Dubai U.A.E.

8th Gulf Seismic Forum, 3-6 March 2013, Muscat-Sultanate of Oman

Outline 1- Goals and Objectives of DSN installation 2- First phase of DSN installation on April 2006 (4BB STS2 +4 Episensor) 2- Real time data exchange with local and regional seismic networks. 3- Second Phase of DSN installation ( 5 strong motion Stations inside Dubai Urban area) + Shake map 4- Seismicity of UAE before and after the DSN installation 5- Source Mechanisms and source parameters of some felt events in the eastern part of UAE 6- Conclusions & Recommendations

Monitoring local and regional earthquakes. Provide local authorities in a real time by all information about felt local and regional earthquakes Identification of the local active seismic zones in U. A. E. Seismic Hazard Assessment. Updating Building Code

The main objectives of DSN

First phase of DSN installation on April 2006

(4VBB STS2 +4 Episensor)

4 X 6-channel broad-band remoteseismic station (RSS)

STS-2

ES-T

Q330

Quanterra Q330

Central Processing SystemDM

Baler PB14F

Radio tower

Spread-SpectrumRadio

Radio tower

Spread-Spectrum Radio

Lease Line Modem

CISCOSYSTEMS

Cisco Router

3 X spread-spectrum radio todigital lease-line repeater

(SSR-DLL)

Digital LL

DSN Overview

Stations Noise Level

Real Time Data Exchange with Local and Regional Seismic Networks

6 BB stations NCMS May 2009

5 VBB stations EMC, Oman May 2007

4 VBB Dubai stations April 2006

1 VBB GSN Saudi VBB (RAYN)

1 VBB GSN Sharjah (UOSS)

17 BB Stations Local /regional

15 GSN VBB Stations

Seismology projects completed by DM 1- Seismic Hazard Assessments and microzoning studies of Dubai Emirate, UAE (June 2008). 3- Dubai Seismic Code (May, 2009)

Second Phase of DSN installation ( 5 strong motion Stations inside Dubai Urban area) & Shake map

Basalt -Strong Motion Data transferred through GPRS technology

Episensor-Strong Motion

GPRS: General Packet Radio Service

Real time Earthquake Notification : SMS & email : sending the earthquake parameters within few seconds for local event (ML> 3) or regional event (mb>5. The parameters are also published on the WEB SITE. In Case of local event (ML> 3) or regional event (mb>5) Shake map is calculated based on the strong motion records or the three component velocity records within few minutes and published on the WEB SITE .

http://www.m1.ae http://www.seismo.geodesy.ae

http://195.229.32.76/~rt/shake/index.html

Historical Seismicity from 184 BC to 1899 AD

After Ambraseys et al., 1994

Seismicity of UAE before and after the DSN installation

Observed Seismicity from 1900 to 1964

After Ambraseys et al., 1994

Observed Seismicity from 1964 to 2006 By ISC

Observed Seismicity from June, 2006 to Dec 2012

Focal Mechanisms for some Felt and Best Recorded Events

Date Time Locations Lat. Long.

H (km) MW Ref.

11 03 2002 20 06 37.2 25.236 56.145 15 4.98 Rodgers et., 2006, Tectonophysics 415, 57-64

10 03 2007 18 15 14.3 25.303 56.191 06 3.66 Al Marzooqi et al., 2008, Tectonophysics 460 (2008) 237–247

13 09 2007 15 47 07.0 25.469 56.297 08 3.94 Al Marzooqi et al., 2008, Tectonophysics 460 (2008) 237–247

12 02 2008 12 02 08.3 25.296 56.205 07 3.70 El-Hussain et al., 2010, 6GSF, Abu Dhabi, UAE

07 05 2009 22 44 00.4 25.401 57.150 15 4.65 El-Hussain et al., 2010, 6GSF, Abu Dhabi, UAE

10 05 2009 01 07 31.6 25.442 57.239 36 3.95 El-Hussain et al., 2010, 6GSF, Abu Dhabi, UAE

08 06 2009 18 13 57.3 25.930 56.501 08 3.87 El-Hussain et al., 2010, 6GSF, Abu Dhabi, UAE

20 02 2011 13 19 10.5 24.916 56.275 05 3.29 Al Khatibi et al., 2012

14 04 2011 13 30 01.7 24.938 56.287 06 3.12 Al Khatibi et al., 2012

21 10 2012 16 10 22.0 25.342 56.252 04 3.8 This Study

09 events

Shake map of October 21, 2012 East Masafi Felt Earthquake

Waveform Inversion Technique

4 BB stations (three-component) in the distance range from 44 to 80 km. The inversion is done in lower frequency band between 0.01 to 0.15 Hz. The matrix inversion method (e.g. Ichinose, 2006) is used to invert for the point source moment tensor using Green’s functions computed for a 1-D velocity model for the Arabian Platform (Rodgers et al., 1999) To account for any origin time and location errors, the synthetics were shifted relative to the observed by changing the origin time few seconds before/after the final location origin time during our inversion.

The inversion is done imposing a deviatoric moment tensor without isotropic component. The Green’s function is computed using a fast reflectivity and frequency-wave number (f-k) summation technique (Zeng and Anderson, 1995). The preferred solution was obtained by a simple grid search over the focal depths between 1 and 10 km with 1 km step.

Source time history was determined by changing the source time function (STF) duration and type (triangular or trapezoidal). The optimal STF was chosen which increased the percent of VR and DC and shows good match between the observed and synthetic waveforms was selected.

VR/DC as function of focal depth and origin time

Event of October 21, 2012 East Masafi Felt earthquake

Observed (solid lines) versus Synthetic (small dashed) displacement waveforms for the preferred focal mechanism.

Interpretation

(Dr. Mohamed Al-Wardi, structural geologist, personal communication) suggest a rectification of the pre-exiting NE to NNE faults as normal faults due to a partly transfer of stress from the collision process. Baker and Fowler (2007?) suggested that the redistribution of stress along the Zendan fault activate the pre-exiting NE-SW faults as normal faults.

Rodgers et al., 2006

NE-SW

N-S

NW-SE

Thrust Normal

Strike slip

Al Marzooqi et al., 2008

Conclusions

The recorded seismic activity from 2006 to 2012 shows three clusters; 1- East of Masafi 2- Wadi Nazwa 3- Northern Huwaylat The two clusters of eastern Masafi and northern Huwaylat are related to NE to NNE reactivated normal faults in the upper crust. While the Activity at Wadi Nazwa are related to the gas storage. The offshore seismicity in the Oman Sea is more or less scattered due to the large Azimuth gap of seismic stations, however it is more likely lies over NE-SW or NNE-SSW Fault trends in parallel to Dibba Fault zone and opposite to the Zendan-Minab Fault System. The focal mechanisms of the well recorded inland small to moderate indicate a normal faulting mechanism with slight right-lateral strike-slip component. Focal depth of inland activity indicate upper crustal activity ~<10 km

Recommendations

Sharing seismic data between Arabian Gulf countries will Enhance location parameters and help to indentify all seismic sources that constitute earthquake hazard on the region.

Sharing strong motion data & Vs30 will helps also to calculate more accurate shake map and will help to derive attenuation relation for the Arabian Peninsula.