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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 M_L=3.5 between 1964 and 1983, and M_L=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	-127.33
	120.02	-118.47
	138.97	-105.02
	163.41	-34.45
	175.88	42.26
Arif	165.01	0.45	E
	166.40	-3.74
	120.76	-23.31
	118.71	-19.48
Paran	165.10	-23.50	A/D	Paran fault, potentially associated with seismicity in the Baraq/Paran fault junction and in Gebel e-Risha
	164.10	-32.30
	46.10	-27.30
	46.30	-17.10
Baraq	174.24	-3.32	A/D	Active Baraq fault, possible related to current seismicity in the Zofar area and the Baraq/Paran fault junction.
	140.62	-58.74
	133.04	-53.31
	166.95	1.44
Milhan	155.00	-52.00	E
	158.50	-56.50
	137.50	-77.00
	133.50	-73.00
East-Central Sinai	86.69	-48.66	C	Area of recent seismicity in eastern Sinai, apparently unrelated to surface faulting.
	120.00	-96.50
	108.00	-105.00
	74.10	-56.90
Thamad	146.26	-97.46	D	Active Thamad fault and seismicity in the overlap with the SW Negev zone.
	146.27	-104.22
	78.44	-100.49
	78.71	-94.16
Elat	138.00	-171.80	A	Northern basin of the southernmost section of the Dead Sea Transform (Gulf of Elat). Intensively active since 1983 and the arrest area of the 1995 Nuweiba earthquake rupture.
	109.52	-161.54
	120.02	-118.47
	152.88	-127.33
Aragonese	143.23	-173.72	A	Central basin of the southernmost section of the Dead Sea Transform (Gulf of Elat). Intensively active since 1983 and the nucleation area of the 1995 Nuweiba earthquake rupture.
	129.94	-215.27
	94.50	-202.50
	109.50	-161.50
Arnona-Dakar	135.30	-217.20	A	Southern basin of the southernmost section of the Dead Sea Transform (Gulf of Elat). Intensively active at least since 1983.
	120.10	-293.80
	72.90	-320.50
	99.20	-204.40
Suez	-109.10	10.70	A/B	The seismically active Gulf of Suez, extending to the seismicity zone of northeast Egypt.
	72.90	-320.50
	-26.30	-345.30
	-175.10	-21.70
Palmira	425.00	550.00	D	Seismically active northern strand of the Syrian Arc fold belt.
	425.00	398.65
	311.35	330.06
	243.48	321.09
	276.94	436.11
North Jordan	312.09	160.10	D	Sporadic seismicity in northwestern Jordan, currently not clearly associated with distinct faults.
	265.00	-0.10
	189.73	2.23
	196.93	28.33
	208.37	66.17
	212.93	125.81
	213.85	229.64
	217.63	260.39
	213.60	266.42
	215.01	287.86
Wadi Sirhan	311.35	330.06	D	Distributed seismicity along the Wadi Sirhan volcanic belt.
	425.00	183.70
	425.00	11.70
	215.01	287.86
	243.48	321.09

4. References

Almagor, G., and Z. Garfunkel, Submarine slumping in continental margin of Israel and Northern Sinai, AAPG Bull., 63, 324-340, 1979.

Arieh, E., D. Artzi, N. Benedik, A. Eckstein-Shapira, R. Issakow, B. Reich, and A. Shapira, revised and updated catalog of earthquakes in Israel and adjacent countries, Inst. Pet. Res. Geophys., Z6/1216/83(3), 1985

Arieh, E., and N. Rabinowitz, Probabilistic assessment of earthquake hazard in Israel, Tectonophysics, 167, 223-233, 1989.

Bartov, Y., Geological photomap of Israel and adjacent areas, 1:750,000, pp., The Geological Survey of Israel, Jerusalem, 1994.

Bartov, Y., A. Sneh, L. Fleischer, V. Arad, and M. Rosenzaft, Catalog and map of young faults in Israel, The Geological Survey of Israel, GSI/23/2000, 2000

Ben-Avraham, Z., Structural framework of the Gulf of Elat (Aqaba), J. Geophys. Res., 90, 703-726, 1985.

Ben-Avraham, Z., G. Almagor, and Z. Garfunkel, Sediments and structure of the Gulf of Elat (Aqaba), Sediment. Geol., 23, 239-267, 1979.

Ben-Avraham, Z., and G. Tibor, The northern edge of the Gulf of Elat, Tectonophysics, 226, 319-331, 1993.

Ben-Menahem, A., Four thousand years of seismicity along the Dead Sea rift, J. Geophys. Res., 96, 20195-20216, 1991.

Ben-Menahem, A., M. Vered, and D. Brooke, Earthquake risk in the Holy Land, Bull. Geof. Teor. Appl., 24, 175-203, 1982.

Fleischer, L., and R. Gafsu, The structural map of Israel - top Judea group, phase 1:Galil and Arava, Geophys. Inst. Isr., 873/68/98, 1998

Fleischer, L., and R. Gafsu, The structural map of Israel - top Judea group, phase 2: Central Israel, Geophys. Inst. Isr., 873/55/99, 2000

Garfunkel, Z., and Y. Bartov, The tectonics of the Suez rift, Geological Survey of Israel, Bull. 71, 1977

GII, S. B., Earthquakes in and around Israel, 1907-2001, Geophysical Institute of Israel, 2000

Heimann, A., and H. Ron, Young faults in the Hula pull apart basin, central Dead Sea Transform, Tectonophysics, 141, 117-124, 1987.

Kempler, D., and Z. Ben-Avraham, The tectonic evolution of the Cyprean Arc, Ann. Tectonicae, 1, 58-71, 1987.

Khair, K., G. F. Karakaisis, and E. E. Papadimitriou, Seismic zonation of the Dead Sea transform fault area, Annali di Geofisica, 43, 61-79, 2000.

Papazachos, B. C., G. F. Karakaisis, E. E. Papadimitriou, and C. A. Papaioannou, The regional time and magnitude predictable model and its application to the Alpine-Himalayan belt, Tectonophysics, 271, 295-323, 1997.

Rotstein, Y., Gaussian probability estimates for large earthquake occurrence in the Jordan Valley, Dead Sea rift, Tectonophysics, 141, 95-105, 1987.

Salamon, A., A. Hofstetter, Z. Garfunkel, and H. Ron, Seismicity of the eastern Mediterranean region: Perspective from the Sinai subplate, Tectonophysics, 263, 293-305, 1996.

Shamir, G., and L. Feldman, Distribution of current microseismic activity in the Hula basin, in Annual Meeting of the Geological Society of Israel, p. Kefar Giladi, 1997.

Shamir, G., Y. Gitterman, Y. Leonov, A. Shapira, B. Reich, L. Feldman, D. Steinberg, and N. Rabinowitz, Shivta-Rogem NPP site investigation: Basic data report no. 12, - Regional and Site Seismicity Analysis, Geophys. Inst. Isr., 546/71/99, 2000

Shapira, A., Potential earthquake risk estimations by application of a simulation process, Tectonophysics, 95, 1983.

Shapira, A., and G. Shamir, Seismicity parameters of seismogenic zones in and around Israel, Institute for Petroleum Research and Geophysics, Z1/567/79(109), 1994

Sneh, A., Y. Bartov, and M. Rosensaft, Geological Map of Israel, pp., The Geological Survey of Israel, Jerusalem, 1998.

Yuceman, S. M., Seismic hazard maps for Jordan and vicinity, Nat. Haz., 6, 201-226, 1992.

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