PRELIMINARY
SEISMIC ZONATION
GSI
Report No. GSI/12/2001 GII
Report No. 550/95/01(1)
March
2001
.___________
by
G. Shamir1,
Y. Bartov2, A. Sneh2, L. Fleischer1, V. Arad2,
M. Rosensaft2
1 The Geophysical
Institute of Israel, Lod
2 The Geological Survey of
Israel, Jerusalem
1.
Introduction
The
definition and characterization of seismogenic zones is a key element in the
process of earthquake hazard assessment and depends on the surface and
sub-surface geometric, kinematic and mechanic properties of active faults (e.g.
slip rate, typical faulting mechanism, return time, etc.), as well as on the
seismicity distribution. Following the determination of zone boundaries, the
seismicity pattern of each zone is calculated, most importantly the frequency-magnitude
relation and maximum magnitude estimation.
The
accuracy and resolution of previous attempts at seismic zonation in Israel have
increased with improvements in earthquake recording and with the resolution of
mapping and kinematic analysis of fault systems. Studies that either emphasized
regional zoning, or relied on limited databases (Ben-Menahem et al., 1982; Shapira, 1983; Rotstein, 1987;
Ben-Menahem, 1991; Papazachos et al., 1997; Khair et al., 2000) used rough zonation, with 2-4 earthquake producing
regions. Arieh and Rabinowitz (1989) subdivided the Dead Sea Transform (DST) into
distinct basin and inter-basin sections, defined second order seismogenic zones
(Carmel, Fara’a) and took into account areas of distributed seismicity
(Mediterranean, Lebanon coast, Galilee). Yuceman (1992) used line sources to represent known (DST, Suez) or
presumed (Mediterranean offshore) fault zones and areas to represent
distributed seismicity (Beka’a, Mediterranean). Shapira and Shamir (1994) presented a detailed seismic zonation of Israel
based on epicenter distribution for earthquakes that occurred since 1907 and
mapped fault geometry, without taking into account the age of faulting. A
distinction should be made between these studies, aimed at defining seismic
sources at the highest possible resolution, and studies delineating the overall
plate boundaries, e.g. Salamon et al. (1996).
The
seismic zonation presented here attempts, for the first time, to integrate the
seismological and geological data accumulated over the last several decades and
to put defined constraints on its usage. Such constraints are based, for
example, on the temporal changes in the completeness of the earthquake catalog
of Israel, and on published determinations of the age of activity along
specific faults. The preliminary seismic zonation presented here should serve
as a framework for long term, iterative multi-disciplinary studies, leading to
modification and refinement of the seismogenic zones.
2.
Data
sources
The
preliminary seismic zone map is based on the following data sources:
(i)
The catalog of
earthquakes in and around Israel (GII, 2001), which covers the period since
1907. Instrumental recording in Israel and adjacent areas began in 1954 with
the installation of seismograph stations in Jerusalem and Zefat. Standard
seismograph stations were established in Jerusalem in 1964 and in Elat in 1969
(operating until 1981) as part of the World Wide Standard Seismograph Network
(WWSSN). The 14-station Israel Seismic Network (ISN) became operational in
September 1981. It currently consists of 24 short period stations, 6 of which
have 3 components, and 7 broadband stations. Additional seismicity data have
been obtained from regional sources, mainly the Ksara (Lebanon) and Helwan
(Egypt) WWSSN stations. A comprehensive revision and updating of the ISN
catalog was presented by Arieh et al. (1985). For the sake of accuracy in
defining seismic zones we chose a cutoff of the data in 1964, when data from
three well calibrated, standard seismographs equipped with synchronized timing
systems became available. Based on Arieh et al. (1985) and Shamir et al.
(2000), the completeness threshold of the earthquake catalog is ML=3.5
between 1964 and 1983, and ML=2.0 since 1983. We use these values to
further sort the data used in this report.
(ii)
The catalog of young
faults in Israel (Bartov et al., 2000;
and references therein). This database includes faults that offset
sedimentary rocks of Pliocene or younger age, volcanic rocks younger than 5 Ma
and faults that have been defined as “young” based on geomorphologic
considerations. The base maps for this database are the 1:200,000 geological
map of Israel (Sneh et al., 1998) and the structural map of Israel (Fleischer and Gafsu, 1998; Fleischer and
Gafsu, 2000).
(iii)
Mapped fault systems
along the seismically active boundaries of the Israel-Sinai sub-plate,
specifically in the Gulf of Elat (Ben-Avraham
et al., 1979; Ben-Avraham, 1985; Ben-Avraham and Tibor, 1993), the Gulf of Suez (Garfunkel
and Bartov, 1977) and in the Roum-Yamune fault system (Bartov, 1994).
3. Seismogenic Zones
The
seismogenic zones presented in this report (Fig. 1) encircle areas that show
recent seismic activity and/or post-Pliocene geological activity. Based on the
spatial distribution of epicenters and reported active faults, the following
classification of seismic zones was defined:
A: Measurable
seismicity clearly associated with active faults.
B: Measurable
seismicity associated with mapped geological structures, which have not been
defined as active in post Pliocene times.
C: Measurable
seismicity with no apparent association with known geological structures.
D: Active faults
and sporadic seismicity with no coherent relation between them.
E: Active
faults with no recorded seismicity associated with them.
Some additional
considerations in defining seismogenic zones are as follows:
(i)
The DST
was subdivided in such a way that basins (Hula/Kineret, Dead Sea, Gulf of Elat
basins) and inter-basin segments (Arava, Jordan Valley) form distinct zones.
The rationale is that basinal sections are characterized by continual, low to
medium magnitude or swarm-type activity, while inter-basin sections have either
been relatively quiescent over the instrumental period (e.g. the Arava) or
ruptured in large earthquakes (the 1995 Nuweiba earthquake). An alternative
approach could be placing zone boundaries halfway in basins, which are the
expression of fault step-over zones. This is based on the observation that the
Nuweiba earthquake nucleated and was arrested within the Aragonese and Elat
basins, respectively.
(ii)
Seismic
zones are defined as area sources, rather than line sources, even where the
fault zone is well defined, both geologically and seismologically. This is due
to the finite width of fault zones (e.g. the Dead Sea Rift), their inclinations
and the inherent hypocenter uncertainty.
(iii)
Where
the exact structural association between earthquake epicenters and specific
fault systems is unclear, overlapping zones were introduced (e.g. Bet
She’an/Gilbo’a-Jordan Valley-Carmel/Tirza, Baraq-Paran).
The
seismic zones defined in this report are listed in Table 1 below, where x,y are
coordinates in the Israel local coordinate system and the zone types refer to
the zone classification above. Some zones, particularly those of type C, D and
E, should be analyzed in the future in order to improve their boundary determination,
fault mapping and to better relate seismicity to geological structures within
them.
Table 1:
List of Seismic Zones.
|
Zone
|
X
|
Y
|
Type
|
Comments
|
|
Cyprus
|
230.60
|
491.10
|
A
|
The Cypriot
Arc (Kempler and Ben-Avraham,
1987)
|
|
28.80
|
427.60
|
|
-124.50
|
403.60
|
|
-200.00
|
449.80
|
|
-200.00
|
550.00
|
|
-107.00
|
507.20
|
|
16.00
|
520.60
|
|
82.10
|
550.00
|
|
232.60
|
550.00
|
|
Mediterranean
|
230.60
|
491.10
|
C
|
Offshore
seismicity in the eastern Mediterranean, to about 200km from the
Israel-Lebanon coast and south of the Cypriot Arc. No information concerning
the fault structure in this zone is currently available.
|
|
114.30
|
133.70
|
|
-137.90
|
220.90
|
|
-124.50
|
403.60
|
|
28.80
|
427.60
|
|
Roum-Yamune
|
280.10
|
550.00
|
B
|
Roum Fault (northward extension of
the Qiryat Shemona Fault) and the Yamune Fault (northward extension of the
Dead Sea transform).
|
|
276.94
|
436.11
|
|
243.48
|
321.09
|
|
215.01
|
287.86
|
|
200.90
|
295.02
|
|
192.98
|
375.37
|
|
230.76
|
370.69
|
|
257.56
|
436.69
|
|
261.80
|
550.00
|
|
Hula-Kineret
|
215.01
|
287.86
|
A
|
Step zone between the Qiryat
Shemona/Roum Fault on the west and the upper Jordan Valley fault on the east.
Includes seismicity in the Hula and Kineret basins and in the Korazim block (Heimann and Ron, 1987; Shamir and
Feldman, 1997)
|
|
213.60
|
266.42
|
|
217.63
|
260.39
|
|
213.85
|
229.64
|
|
199.26
|
233.86
|
|
200.90
|
295.02
|
|
Galilee
|
200.60
|
280.00
|
D
|
Published active faults and
sporadic seismicity therein, bounded by the DST faults of the Hula-Kineret
zone on the east, the Carmel-Tirza fault on the south and the Mediterranean
zone on the west.
|
|
199.26
|
233.86
|
|
197.60
|
210.10
|
|
160.90
|
248.70
|
|
164.00
|
279.70
|
|
Jordan Valley
|
213.90
|
229.61
|
A
|
Inter-basin section of the Dead Sea
transform between the Kineret basin in the north and the Dead Sea basin in
the south.
|
|
212.93
|
125.81
|
|
192.16
|
138.51
|
|
199.26
|
233.86
|
|
Bet She’an-
Gilbo'a
|
203.40
|
203.80
|
A/D
|
Active faults in the Samaria and
eastern lower Galilee
|
|
202.30
|
169.80
|
|
196.70
|
138.70
|
|
178.30
|
153.00
|
|
182.90
|
225.50
|
|
Carmel-Tirza
|
203.40
|
204.00
|
A/C
|
The seismically active Carmel-Tirza
fault from the Lower Jordan valley in the SE to beyond its bathymetric scar
in the Mediterranean in the NW.
|
|
202.40
|
169.80
|
|
90.90
|
290.90
|
|
107.90
|
304.00
|
|
Central Israel
|
182.30
|
84.60
|
C
|
Undefined seismicity in central
Israel, between the northern Dead Sea and the southern Israel coast, with
apparent (but unproven) extension to the offshore Palmahim seismic structure (e.g. Almagor and Garfunkel, 1979;
Garfunkel, 1984).
|
|
179.10
|
63.00
|
|
123.90
|
89.10
|
|
66.90
|
147.10
|
|
86.00
|
169.50
|
|
Dead Sea
|
212.93
|
125.81
|
A
|
Comprises the Dead Sea pull-apart
basin at the step between the Jordan Valley and the Arava segments of the
DST.
|
|
208.37
|
66.17
|
|
196.93
|
28.33
|
|
175.88
|
42.26
|
|
184.40
|
98.15
|
|
192.16
|
138.51
|
|
Arava
|
196.93
|
28.33
|
A/D
|
|
|
152.88
|
|