Transcript COUNTRY REPORT ON Jordan seismological Observatory

COUNTRY REPORT
ON
Jordan seismological
Observatory (JSO) Network
Name of Participant: Engineer
Ahmad Algazo
Name of Organization: Jordan
Seismological Observatory.
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SEISMIC OBSERVATION IN JORDAN
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By: AHMAD ALGAZO
Introduction
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The rate of seismic activity in Jordan is moderate, however many of the strong seismic
events are located along the axis of Dead Sea Rift, which is formed the northwestern
boundary of the Arabian plate. Matching magnetic anomalies across the rift has indicated
a total strike-slip movement of approximately 107-km.
The Jordan Seismological Observatory began routine operation in September 1983.
Seismic data being transmitted via radio on assigned frequencies to the Natural Resources
Authority building in Amman from 26 short periods stations cover all areas in Jordan
Figure (3), also 13 stations have been installed recently in Jordan by using VSAT system
two of them are Broad Band and eleven are short period stations, there is Auxiliary Broad
Band Station for the Comprehensive Test Ban Treaty Organization ( CTBTO ). In addition
there is a Strong Motion Network which consists of 26 digital accelerographs deployed in
the main cities and dams Figure (4).
The earthquake location program SEISAN is used for the routine location of hypocenters,
in addition to the velocity-depth model which shows a p-velocity average for the upper
sedimentary of 3.5 km/sec, and the crust is underlain by a normal mantle with a p-velocity
of 8.00 to 8.2 km/sec.
The Seismological Observatory is issued annual bulletin about the event activity
(Earthquake in Jordan and Adjacent Areas), which are reported to the adjacent
Observatories and to the International Seismological Center.
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Discussion
The Dead Sea Rift zone extends northward from the northern end of the Red Sea for a distance
in excess of 1000 km. Several linear topographic fault controlled depressions are present along
a great portion of this fault zone. Within the purview of plate tectonics, the Dead Sea Rift is a
transform plate boundary connecting the Red Sea, Where crustal spreading is occurring,
northward to a zone of plate convergence. The Arabian plate lies to the east of the rift whereas
on the west several smaller plates, the largest of which is Sinai micro plate, from a part of the
larger African plate (Figure 1).
Although the geology of Jordan is mapped and quite well known, the pattern of earthquake
activity, in particular, its temporal and spatial characteristic and its relationship to the geologic
and tectonic framework of Jordan have not well documented; this is primarily due to the
absence of a seismograph network in Jordan.
Studies of the Seismicity, however, suggest results which are not compatible with the inferred
rate of slip that is occurring along the Dead Sea Rift plate boundary (Freund et al., 1968). On
the other hand, geological and magnetic evidence point to a relative rate of plate movement of
4 - 6 mm/yr along the rift boundary (Girdler and Styles, 1974; Hatcher et al., 1981), and a total
strike-slip movement of approximately 107 km has been indicated by matching magnetic
anomalies across the rift. However, the rate of slip calculated from seismic data as a function
of time yields an average slip rate of only 1 - 3 mm/yr (Kovach, 1979; Ben-Menahem, 1981). One
is therefore forced to conclude that the region is probably accumulating strain energy for a
future large earthquake. Other explanations, that the opening of the Red Sea has slowed
significantly in historic time or that strain is being released as a seismic slip (North, 1974), or
distributed slip is taking place (Kovach et al., 1985), are considered less likely.
Clues to the pattern of Seismicity can be gleaned from the historical record, and a large
amount of literature is available for careful scrutiny. Three sources of data include:
Earthquake listings or catalogs.
descriptions of specific events,
Inferences from archaeological excavations.
Earthquake listings have been presented by Alsanawi and Ghalib
• 1975, Ambrayseys (1961, 1962), Ambrayses and
Melville (1982), Amiran (1950, 1951), Arieh (1967,
1985), Ben-Menahem (1979), Poirer and Taher (1980),
Poirer et al., (1980).
• Most of the seismic events are located along the axis
of the Dead Sea Rift. These events, together with
recent micro earthquake data, point to recurrence
interval; of about 120 years for an Ml = 6.0
earthquake along the rift. Verd (1978) has utilized the
geologic record of total fault displacement and the
rate of seismic activity to estimate that the maximum
expected earthquake along the rift zone would be the
range Ml = 7.5 - 8.0.
Figure ( 1 ): Tectonic Map of the Dead Sea rift region.
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Seismicity
The Dead Sea rift is a transform boundary between the Arabian and African plates,
connecting the Red Sea spreading center in the south to the Taurus-Zagros collision
zone in the north. The Dead Sea transform is about 1100 km. long, and separates the
Sinai sub plate from the Arabian plate. A geological offset of about 105-110 km.
(Quennell 1959; Freund et. al., 1970), has been accumulated along the transform
since the Miocene at a mean rate of left lateral strike slip of ~ 5 mm/year. The Dead
Sea transform is comprised of a series of en echelon main faults, forming pull-apart
basin, among them the Dead Sea basin (Garfunkel et al., 1981; Ben –Avraham, 1985;
and many others). Although the Dead Sea transform is the main source of the
seismic activity in the Dead Sea region, there are highly populated areas within the
neighborhood of active fault systems that branch off the Dead Sea transform, such
as Carmel, Al-Karak Al-Fiaha, Wadi El-Sirhan, Zarqa Main, and Swaqa faults.
The seismicity of the Dead Sea region is considered low to moderate, nevertheless
some destructive earthquakes have been occurred and destroyed most of the urban
areas in Jordan and Palestine, such as 362, 748, 1034, 1070, 1201, 1759, 1837, 1927,
1995, and others earthquakes, with magnitude greater than 6.0 degrees in Richter
scale.
After about 20 years of continuous operation of the seismic networks operated in
the region about 9000 earthquakes were recorded in the region as shown in the
seismicity map Figure.(2) , and as the map shows, most of the mapped faults in the
region are active.
The most populated areas of the Dead Sea region are vulnerable to strong
earthquakes, that will most definitely occur in the future in this region along the
Dead Sea fault system, which will be a major threat to the safety, social integrity and
economics for the peoples of region.
Earthquake hazard assessment no longer refers to single parameters such as the
horizontal peak ground acceleration (PGA) as a quantifier of the hazard. The modern
construction engineer requires information about the expected acceleration at
frequencies similar to the natural frequencies of the building under design. To
provide such
• information we have to know the attenuation laws of ground
motion at different frequency bands. These attenuation laws
should preferably be obtained experimentally. However,
empirical attenuation function can only be developed in the
region that well instrumented (Accelerographs) and exposed to
frequent occurrence of relatively strong earthquakes.
• The only remedy to earthquake loss is proper planning and
building, using the right building code “Earthquakes do not kill
people – houses do! ".
Figure ( 2 ): Seismicity map of the Dead Sea rift region during the period 1983-2008.
Figure ( 3 ) : Jordan Telemetric Seismic Network Stations.
Figure ( 4 ) : Jordan Strong Motion Network Stations.
Abu Dees
Jericho
Jerusalem
Jordan river
Nablus
Jericho