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Isr. J. Earth Sci.; 54: 1–14
© 2005 Science From Israel/ LPPLtd. 0021-2164/05 $4.00
E-mail: begin_bz@mail.gsi.gov.il
Temporal and spatial variations of microearthquake activity along the
Dead Sea Fault, 1984–2004
Ze’ev B. Begin and Gideon Steinitz
Geological Survey of Israel, 30 Malkhe Yisrael Street, Jerusalem 95501, Israel
(Received 6 January 2004; accepted in revised form 28 October 2004)
ABSTRACT
Begin, Z.B. and Steinitz, G. 2005. Temporal and spatial variations of microearth-
quake activity along the Dead Sea Fault, 1984–2004. Isr. J. Earth Sci. 54: 1–14.
Patterns of spatial and temporal variations in microearthquake activity during 1984–
2004 were studied in five segments along the Dead Sea Fault (DSF). In each segment
there is a narrow zone in which intense seismic activity is concentrated; the most
active one is the Dead Sea segment. Segments are also characterized by distributions
of hypocenter depths, with the northern Arava and Dead Sea showing the deepest
hypocenters.
The annual distribution of earthquakes is nonuniform in all segments, with years of
peak activity occurring between 1989 and 1992 in the different segments. The maxi-
mum annual number for the DSF as a whole was 215 earthquakes (M
L
≥ 0) in 1991,
while in 1984 and in 2001 the number of earthquakes was only about 70. The
cumulative seismic moment for the DSF decreased exponentially from 1984 (2⋅10
22
dyne cm) to 20% of that value in 2003 and then increased by two orders of magnitude
in 2004. During 1995–2004 the changes in the annual number of earthquakes were
concomitant with changes in the average annual Rn concentration, as measured close
to the active boundary fault in the NW Dead Sea. In southern Israel and Jordan, where
only few earthquakes had occurred between 1984 and 1995, a marked increase in
seismic activity took place after the 1995 Nuweiba earthquake in the Gulf of Elat.
INTRODUCTION
The Dead Sea Fault (Transform) is an active fault zone
forming the Arabian–Sinai plate boundary, stretching
from the spreading Red Sea to the Eastern Anatolian
Fault. All along the Transform it is accompanied by a
conspicuous rift valley. Based on considerations of
plate kinematics and matching of structures across the
Fault (summarized by Garfunkel, 2001), it is generally
accepted that the principal sense of movement along
the Fault has been left lateral, with a total slip of 105
km (Quennel, 1959; Freund, 1965; Freund et al., 1970;
Garfunkel et al., 1981; Garfunkel, 2001). According to
a different view, the horizontal slip along the Dead Sea
fault is smaller (Mart, 1991; Horowitz, 2001), amount-
ing to 10–20 km (Mart et al., 2005).
The average horizontal slip rate along the Dead Sea
Fault (DSF) during the last 5 Ma was determined to be
6–7 mm/year, based on plate kinematics (Joffe and
Garfunkel, 1987; Garfunkel, 2001). Along the middle
and northern Arava segment of the DSF, several esti-
mates of horizontal slip rates were suggested, based on
2 Israel Journal of Earth Sciences Vol. 54, 2005
displaced alluvial fans, terraces, and gullies: 3–7.5 mm/
year during the last 5–2 Ma (Ginat et al., 1998); 4 ±
2 mm/year during the last 70,000–140,000 years and
5 ± 1.2 during the last 2,000–3,000 years (Klinger et al,
2000); 4.7 ± 1.3 mm/year during the last 15,000 years
and 3.9 ± 0.5 during the last 6,000 years (Niemi
et al., 2001). In the Missyaf segment of the DSF in
Syria, north of the Yammuneh restraining bend, a
displaced aqueduct shows a slip rate of 7 mm/year
during the last 2000 years (Meghraoui et al., 2003).
Based on GPS measurements, the current slip rate
along the DSF is 3.3 ± 0.4 mm/year (Wdowinski et al.,
2004).
A century-long record that includes strong earth-
quakes shows that the moment released by the ob-
served earthquakes along the DSF did not account for
more than 2 mm/year of the rate of relative motion
across the Transform (Ben-Menahem, 1981;
Garfunkel et al., 1981; Salamon et al., 2003; Shapira et
al., 2004). Noting that in these calculations the mo-
ments were added regardless of the actual direction of
movement on particular faults (Salamon et al., 2003),
this is a maximum value. Deficiency in seismic mo-
ment along the Dead Sea Fault is also shown for the
period 70–14 ky BP in the record of the Lisan Forma-
tion, by the meagerness of strong earthquakes (Marco
et al., 1996; Begin et al., 2005), as well as in the record
of damaged cave deposits in the Soreq Cave, 40 km west
of the Dead Sea (Kagan et al., 2005). Thus, the seismic
activity accounts for only a part of the movement along
the DSF.
Of the earthquakes that occurred along the DSF in
the last 20 years about 99% were of a magnitude <4,
and one should be cognizant of the fact that the rela-
tionship between such small seismic events and the
seismotectonic regime along the DSF is not at all
obvious. This problem is examplified by the fact that
in spite of the overwhelming evidence for a left-lateral
movement along the DSF, several fault-plane solu-
tions along it (carried out for M
L
≥ 4 earthquakes)
indicate other mechanisms and directions of move-
ment, some attesting to normal faulting and hence
extension in a direction perpendicular to the DSF di-
rection. The expected main component of left-lateral
motion on NNE-striking faults along the DSF is found
in the fault-plane solutions for the strongest events, in
1927 and in 1995 and their aftershocks (Salamon et al.,
2003). On top of these problems, the present study is
based on an instrumental record that is only 21 years
long and the limitations on the ability to draw pertinent
tectonic information from this short period are clear.
On the other hand, the importance of micro-
earthquakes should not be dismissed hastily. Their
analysis reveals regular patterns that are characteristic
of tectonic provinces (Wesnouski, 1990; Stirling et al.,
1996), and it has also been shown that a rise in the
seismic rate of small earthquakes may herald a strong
earthquake (Shapira, 1990; Bowman et al., 1998).
Time-dependent seismic behavior of strong earth-
quakes along the DSF has been shown on the scale of
tens of thousands of years (Marco et al., 1996; Begin et
al., 2005), thousands of years (Amit et al., 1995;
Leonard et al., 1998; Zilberman et al., 2000; Amit et
al., 2002), and hundreds of years (Migowski et al.,
2004). Seismic characteristics of segments along the
DSF, based on short records of microearthquakes,
have been discussed previously (Wu et al., 1973; Arieh
and Rotstein, 1985; Rotstein and Arieh, 1986; Shapira
and Feldman, 1987; van Eck and Hofstetter, 1989,
1990; Hofstetter et al., 1996). However, these short-
term analyses did not permit presentation of temporal
patterns in the rate of seismic activity along the DSF.
Here we report temporal patterns in the rate of
microearthquake seismicity on the scale of years, after
two decades of meticulous data gathering of mi-
croearthquakes in this region by the Seismology Divi-
sion of the Geophysical Institute of Israel.
METHOD
In some previous studies that addressed seismicity
along the DSF, the area between the Gulf of Elat and
the Baqaa in Lebanon was subdivided into two seg-
ments: a northern segment, which either includes the
southern Dead Sea (Ben-Menahem, 1991; Yücemen,
1992) or excludes it (Khair et al., 2000), and the Arava
segment. In other studies a more detailed subdivision
was employed, based on geological considerations.
Since the DSF comprises pull-apart grabens and seg-
ments between them that are structurally higher
(Heimann, 1990; Garfunkel, 1997; Frieslander and
Bartov, 1997), in the studied area the DSF lends itself
to a natural subdivision into four segments (Arieh and
Rabinowitz, 1989; Shamir et al., 2001): The Arava
structural high, the Dead Sea pull-apart, the Jordan
valley structural high, and the Kinneret–Hula pull-
aparts. In an attempt to furnish more detail on the
120-km-long Arava segment, we divided it further into
northern and southern segments with the border be-
tween them in the Arava water divide (Fig. 1).
The earthquake data set for the study area (Fig. 1)
was taken from the Israeli earthquake catalog for 2004
Z.B. Begin and G. Steinitz. Dead Sea Fault earthquake activity, 1984–2004 3
(www.gii.co.il/html/seis/seis_search.html), as pub-
lished by the Seismology Division of the Geophysical
Institute of Israel, which operates the Israel Seismic
Network (ISN). The magnitude threshold of complete
record for the area along the DSF is, since 1986,
M
L
≥ 2.0 (Shapira, 1992); for 1984–1985 the threshold
is M
L
≥ 2.5 (Shapira, 2002, appendix A). Although the
ISN was installed in 1980, the record analyzed here
starts in 1984, taking into account initial difficulties
in the ISN operation. The magnitude–frequency rela-
tionship (Fig. 2) shows that this study deals with
microearthquakes.
The presentation of the results starts with general
considerations: a description of the spatial distribution
of earthquakes, the adequacy of the data set, and the
temporal nonuniformity of the time series for the DSF
as a whole. We then proceed to describe in each seg-
ment the temporal patterns of two aspects of seismic-
ity: number of earthquakes and seismic moment.
RESULTS
A. General considerations
Spatial clusters
As already noted, on the basis of few years of
observations (van Eck and Hofstetter, 1989, 1990;
Shapira, 1990), the spatial distribution of microearth-
quakes along the DSF is nonuniform. Five spatial
Fig. 1. Earthquakes (M
L
≥ 2) during 1984–2004 along the
DSF and near it, classified according to their magnitude
(M
L
), shown on the backdrop of faults that are potentially
active (Bartov et al., 2002). Rectangles are segments used in
this study; from bottom: (1) southern Arava (135/–120 to
175/–030), (2) northern Arava (155/–030 to 200/040), (3)
Dead Sea (175/040 to 215/140), (4) Jordan Valley (190/140
to 215/230), (5) Kinneret (190/230 to 215/300). Grey area
denotes the Dead Sea rift valley.
Fig. 2. Cumulative magnitude–frequency diagram for earth-
quakes in the five segments along the DSF (Fig. 1). Data are
based on periods with complete records: since 1900 for
M
L
≥ 5, since 1940 for M
L
≥ 4, and since 1984 for M
L
≥ 2.
The resulting b-value is 0.96.
4 Israel Journal of Earth Sciences Vol. 54, 2005
clusters, one in each segment, are revealed in Figs. 3
and 4. Measured along the north–south direction, the
width of these clusters comprises only some 10% of
the rift length, but more than 20% of the earthquakes
that occurred in 1984–2004 are concentrated in them.
In the Arava, Dead Sea, and Jordan valley segments
(Fig. 1) the locations of these clusters coincide with
junctions of the DSF with transversal faults: The
Thamad fault in the Southern Arava, the Paran–Arif
fault in the northern Arava, an E–W fault east of the
Dead Sea, and the Faria fault in the Shomeron (see also
Aldersons et al., 2003, fig. 1).
The five segments also show characteristic distribu-
tions of hypocenter depths (Fig. 5), despite the large
error in their determination and recognizing that depth
was truncated in the determination algorithm at 25 km
(A. Shapira, personal communication, 2004). Charac-
terizing the depth distributions by their medians, the
northern Arava and Dead Sea segments are similar
(median depth = 11.5 km), the southern Arava has
shallower hypocenters (median = 9.5 km), and the Jor-
dan valley and Kinneret segments show still shallower
hypocenters (median depths of 9 km and 7.5 km, re-
spectively). The differences between the depth distri-
butions of the northern Arava and Dead Sea segments
and those of the three other segments are significant at
the p < 10
–5
level (Fig. 5). Except for the southern
Arava segment, this trend corresponds to the south-to-
north thinning of the crust by 5 km along the DSF
(Aldersons et al., 2003).
Earthquake doublets
Earthquake “doublets” are those that occur a short
time (here defined as less than one day) after a previ-
ous earthquake. “Doublets” might spuriously affect
the analysis of the annual number of earthquakes be-
cause some of them are dependent on the occurrence
of earthquakes that immediately precede them. To ex-
Fig. 3. A space–time diagram showing seismic activity along
the DSF, 1984–2004, for all recorded earthquakes. Note
clustering of earthquakes in narrow zones within each seg-
ment. Segment numbers in right-hand column correspond to
Fig. 1.
Fig. 4. Distribution of earthquakes along the DSF, for 1984–
2004. Discussed segments are indicated. Bin size is 10 km.
A: M
L
≥ 0. B: M
L
≥ 2. The figures are quite similar, but with
the smaller earthquakes the clustering along the DSF is more
pronounced.
A
B
Z.B. Begin and G. Steinitz. Dead Sea Fault earthquake activity, 1984–2004 5
Fig. 5. Depth of hypocenters in the five segments along the
DSF for the period 1984–2004, depicted by the cumulative
percent of earthquakes in each segment. The differences
between the depth distributions in the Dead Sea and northern
Arava segments, with a median of 11.5 km, are significantly
different (p < 10
–5
, tested with the Mann–Whitney test) from
the depth distributions in the segments of the Kinneret (me-
dian = 7.5 km), the Jordan valley (median = 9 km), and the
southern Arava (median = 9.5 km).
Fig. 6. For all earthquakes during 1984–2004 in the five segments along the DSF: A–B: Occurrence of distance to previous
earthquake (D
p
) for two different time intervals to previous earthquake (T
p
). About 30% of earthquakes with T
p
< 1 day are
found at D
p
< 5 km. Bin size is 5 km. C–D: Occurrence of time intervals to previous earthquakes (T
p
) for two different distances
to previous earthquake (D
p
). About 70% of the earthquakes with D
p
< 5 km have a T
p
< 0.5 day, while for D
p
> 5 km only 25%
are within that time interval. Bin size is 0.5 day.
amine this issue, the difference (T
p
) between the occur-
rence time of an earthquake and the occurrence time of
an immediate previous one was calculated, as well as
the distance (D
p
) between the locations of the two
earthquake epicenters. The data set was subdivided
into two subsets: one with T
p
<1 day (Fig. 6A) and the
other with T
p
≥ 1 day (Fig. 6B). It is seen that for
earthquakes with T
p
< 1 day the modal D
p
is 0–5 km.
The same data set was further subdivided into D
p
results
in two different subsets: one with D
p
< 5 km (Fig. 6C)
and the other with D
p
≥ 5 km (Fig. 6D). These subsets are
quite distinct: Only 20% of earthquakes with D
p
≥ 5 km
occurred within T
p
< 0.5 day, while about 70% of the
earthquakes with D
p
< 5 km occur within that time
interval, indicating a correlation between consecutive
earthquakes that occur within a short distance from pre-
vious ones. The percent of earthquakes with D
p
< 5 km
increases with the annual number of earthquakes
(Fig. 7B).
Nonuniformity of the earthquake time series
Only earthquakes with M
L
≥ 2.0 are fully repre-
sented in the catalog, and the percent of earthquakes
6 Israel Journal of Earth Sciences Vol. 54, 2005
with M
L
< 2.0 increases with the annual number of
earthquakes (Fig. 7A). In the following analyses we
included all earthquakes that are registered in the cata-
log, assuming that the total number provides an indica-
tor for the seismic activity.
Considering only earthquakes with M
L
≥ 2.0 and
D
p
> 5 km, which may be viewed as the “harder core”
of the data, the temporal nonuniformity is obvious
(Fig. 7C). For earthquakes with M
L
≥ 3.0, the com-
pleteness of the record along the DSF allows us to
extend the time series back to 1964 (Shapira, 2002).
Although the total number of these earthquakes is
small (Fig. 7D), it is possible to compare their numbers
in the first 20 years of this period (1964–1983, 30
earthquakes) to the latter 20 years (1984–2003, 114
earthquakes, even without considering 2004 with its
exceptionally high number of M
L
≥ 3.0 earthquakes)
and to test through the χ
2
test the probability of random
occurrence of such deviation from the long-term aver-
age (p < 0.0001). We may conclude that on a decadal
scale the nonuniformity of the time series of annual
number of earthquakes is a real attribute of the seismic
behavior along the DSF during the studied period.
B. Number of earthquakes
Annual distribution of earthquakes
Incorporating all earthquakes (M
L
≥ 0) within the
studied area, the time series for the different segments
is presented in Fig. 8. In each of the segments, the
distribution of earthquakes in time is significantly
Fig. 7. For all segments. A: The increase in the percent of earthquakes having M
L
< 2 with increasing annual number of
earthquakes having M
L
≥ 0 (1984–2004). p is the probability of random occurrence of the correlation coefficient r. B: The
increase in the percent of earthquakes having D
p
< 5 km with increasing annual number of earthquakes having M
L
≥ 0 (1984–
2004). C: The temporal nonuniformity of earthquake occurrence along the DSF, for earthquakes having M
L
≥ 2 and D
p
≥ 5 km.
Cubic polynomial fit is statistically significant. Horizontal line shows the average for this period. D: The temporal nonuni-
formity of earthquake occurrence along the DSF, for the complete record of earthquakes having M
L
≥ 3 for 1964–2004, with a
5-year running average. Horizontal line shows the average for this period.
Z.B. Begin and G. Steinitz. Dead Sea Fault earthquake activity, 1984–2004 7
different from a random one. The timing of the
maxima of annual earthquake occurrence in the five
segments changes slightly between 1989 and 1992; the
maximum for the DSF as a whole is in 1991.
Earthquakes in the southern Arava and adjacent areas
After the 22 November 1995 Nuweiba earthquake
(Shamir et al., 2003), a remarkable increase in seismic-
ity is discerned, mainly NW and NE of Elat, more than
100 km north of the earthquake epicenter (Fig. 9). In
these areas faults trending NW and NE, respectively,
are not known. There was a marked increase in seis-
micity NW of Elat immediately after the Nuweiba
earthquakes and a small increase in seismicity NE of
Elat a year after that earthquake (Fig. 10), whereas in
the southern Arava many earthquakes occurred before
the Nuweiba earthquake. However, an increase in the
number of earthquakes in the southern 50 kilometers
of the Arava after the Nuweiba earthquake can be
clearly seen in the bottom of Fig. 3. We propose that
redistribution of stress following the Nuweiba earth-
quake is the cause of the increased seismicity in south-
ern Israel and Jordan during 1995–1998.
Rate of seismicity and Rn concentration at the NW
Dead Sea
Radon concentration has been measured near the
western boundary fault in the northwestern Dead Sea
since 1995. A statistically significant connection be-
tween anomalies in Rn concentration and earthquakes
Fig. 8. Changes in the annual number of earthquakes (M
L
≥ 0) along the DSF during 1984–2004. Temporal trends are
illustrated through polynomial fits (quadratic polynomials for the southern Arava and Jordan valley segments, cubic polynomials
for the Dead Sea and Kinneret segments, as well as for all segments together). p denotes the statistical significance of the fits.
8 Israel Journal of Earth Sciences Vol. 54, 2005
Fig. 10. A, B, C—quarterly earthquake
(M
L
≥ 0) occurrence in the three areas
depicted in Fig. 9, respectively, showing
an increase in the number of earth-
quakes after the Nuweiba 1995 earth-
quake in the Gulf of Elat. D—quarterly
occurrence of earthquakes with M
L
≥ 4
in the Gulf of Elat for the period 1980–
2004.
Fig. 9. Earthquakes (M
L
≥ 0) in the southern Negev and Jordan for the period 1984–2004, classified according to their time of
occurrence relative to the Nuweiba earthquake in the Gulf of Elat, 22 November 1995. Histograms of quarterly earthquake
occurrence in areas A, B, and C are shown in Fig. 10. In areas A and C most earthquakes occurred after the Nuweiba
earthquake.
Z.B. Begin and G. Steinitz. Dead Sea Fault earthquake activity, 1984–2004 9
in the Dead Sea and Kinneret basins has been pre-
sented (Steinitz et al., 2003). Here (Fig. 11), a statisti-
cally significant relationship between the annual num-
ber of earthquakes along the DSF and the annual
average of Rn concentration is presented for the period
1995–2004. This correlation is quite remarkable, re-
membering that Rn concentration varies seasonally
(Steinitz et al., 2003) and that the record pertains to
only one station in the NW Dead Sea, while the num-
ber of earthquakes is recorded along the whole Dead
Sea Fault, 200 km north and south of the Rn monitor
(see also the Discussion below).
Seismic activity and fault offset
The seismic activity along five California strike-
slip faults was shown to be inversely proportional to
the overall fault displacement (Wesnousky, 1988).
Seismic activity was measured as the number of earth-
quakes with M
L
≥ 3 that occurred in 55 years per km of
fault length, normalized per 1 mm of Holocene slip. In
order to permit comparison to the DSF, seismicity is
further normalized here per year, taking the DSF com-
plete record for M
L
≥ 3 of 41 years (1964–2004). The
DSF fits well within the California scheme (Fig. 12).
C. Seismic moment
For 418 earthquakes in the area of study, seismic mo-
ment (M
0
) values appear in the ISN catalog, being
determined according to the method presented in
Shapira and Hofstetter, 1993. These were used in order
to estimate seismic moment for all other earthquakes
studied here, by regressing log M
0
on magnitude, M
L
(Fig. 13). For the range 0 ≤ M
L
≤ 5.2 the relationship is
well represented by the quadratic equation: log M
0
=
18.46 + 0.177 M
L
+ 0.160 M
L
2
. A similar relationship
was found for California earthquakes (Hanks and
Boore, 1984; Ben-Zion and Zhu, 2002), and for earth-
quakes in the DSF, the upward curvature of this non-
linear relationship is implied by the findings of
Hofstetter et al. (1996, fig. 7). From a linear regression
of log seismic moment on earthquake magnitude, for
the range 4 < M
L
< 6.7, Shapira and Hofstetter (1993)
obtained the regression equation: log M
0
= (16.0 ± 0.4)
+ (1.5 ± 0.1) M
L
. This calculation underestimates the
seismic moment of earthquakes with M
L
> 5.5; for
M
L
> 6 it underestimates M
0
by more than 50%.
The annual seismic moment for the 425-km-long
DSF studied here (Fig. 14) shows a significant expo-
nential decrease during 1984–2003. On average, the
cumulative seismic moment along the DSF in 2003
(5.3⋅10
21
dyne cm) was only 20% of the seismic mo-
ment in 1984. For certain time intervals, in the Arava
segments statistically significant (p < 0.05) exponen-
tial decrease in annual seismic moment release can be
traced, while in the Kinneret segment an increase is
discerned (Fig. 14); no trend is apparent in the Dead
Fig. 11. A—Annual number of earthquakes (M
L
≥ 0) in the DSF and annual average Rn concentration measured in the
northwestern Dead Sea (Steinitz et al., 2003), 1995–2004. B—Correlation between annual number of earthquakes in the DSF
and annual average Rn concentration measured in the northwestern Dead Sea. p is the probability of random occurrence of the
correlation coefficient r.
10 Israel Journal of Earth Sciences Vol. 54, 2005
Fig. 13. The relationship between log seismic moment (dyne
cm) and M
L
as determined for 418 earthquakes in the five
segments along the DSF (Fig. 1), showing a significant
quadratic relationship.
Fig. 12. The statistically significant correlation between fault offset and the annual number of earthquakes (M
L
≥ 3) per km of
fault length, normalized per 1 mm of annual slip rate, modified after a relationship originally proposed by Wesnouski (1990).
Data points 1–5: Southern California strike-slip faults for 1932–1986 (Wesnousky, 1990). 1. Neweport-Inglewood. 2. San
Jacinto. 3. Elsinore. 4. Garlock. 5. San Andreas. For (1) and (3), the offset is presented as the geometric mean of two extreme
estimated values (Wesnousky, 1990, table 1). Data point 6: the Dead Sea strike-slip fault (1964–2004). p is the probability of
random occurrence of the correlation coefficient r.
Sea and Jordan valley segments. For the 21 years
studied here, the cumulative seismic moment along the
DSF is presented in Table 1, showing the change in the
distribution of seismic moment between segments that
took place after the M
L
= 5.2 earthquake of 11.2.04.
DISCUSSION
The data presented above for 1984–2004 show some
regularity in temporal trends in the seismic activity
along the DSF, both in the annual number of earth-
quakes and in seismic moment. Although the centers
of seismic activity in the five segments are 50–100
kilometers apart and the earthquakes are very small,
the timing of the peaks of earthquake activity is simi-
lar, within a range of two years (1991–1992) in four of
the five segments and within a range of four years
(1989–1992) in all of the five segments. Simulating a
random process, the probability was calculated of ran-
domly obtaining a situation in which all five segments
have their maximum number of earthquakes in any 4-
year window within 21 years of measurements. The
resulting probability is < 0.004 (we thank D. Steinberg
Z.B. Begin and G. Steinitz. Dead Sea Fault earthquake activity, 1984–2004 11
Table 1
Annual seismic moment (dyne cm) for the period 1984–2004
Segment Annual average of seismic moment × 10
22
dyne cm Seismic moment × 10
22
dyne cm
(Fig. 1) 1984–2003 during 2004
Southern Arava 0.2 0.05
Northern Arava 0.2 0.02
Dead Sea 0.4 66.5
Jordan valley 0.8 8.5
Kinneret 0.2 0.2
Fig. 14. Annual changes in seismic moment release (dyne cm) for 1984–2004. The lines show time intervals in which there is
a statistically significant exponential change in seismic moment; p is the probability of random occurrence of correlation
coefficient r. Note significant multi-year decrease in seismic moment for the DSF (Fig. 14A) during 1984–2003. Most of the
seismic moment released in 2004 is due to M
L
5.2, 4.7, and 4.3 that occurred during February–July.
12 Israel Journal of Earth Sciences Vol. 54, 2005
for the simulation). This indicates the operation of a
mechanism that drives common earthquake activity
along the DSF. This conclusion is supported by the
gradual and consistent decrease of seismic moment for
20 years, during the period 1984–2003.
Such common mechanism is also indicated by the
10-year correlation between the annual number of
earthquakes along the whole DSF and the average Rn
concentration, as measured in one point, within the
Dead Sea segment. It should be noted that many Rn
anomalies in the Dead Sea area are not the result of
earthquakes. Rather, they were shown to precede
earthquakes and were interpreted as signifying tran-
sient stress along the DSF (Steinitz et al., 2003).
Hence, a change in annual Rn concentration seems to
indicate a change in the frequency of occurrence of
stress transients. This leads us to assume that the de-
crease in number of earthquakes along the DSF during
1995–2000 and its increase during 2001–2004 do not
signify an availability of fault planes that are ready to
yield while the regional stress remains constant.
Rather, they reflect general changes in stress.
As it is assumed that most of the smaller earth-
quakes along the DSF are an expression of normal
faulting that is secondary to the main strike-slip move-
ment on the DSF, it is intriguing to realize that their
activity does reflect a large-scale tectonic process
driven by a common source along the 400-km-long
segment of the DSF.
The 20-year decrease in seismic moment and the
decadal decrease in number of earthquakes along the
DSF preceded the M
L
= 5.2 earthquake in the NE Dead
Sea on 11 February 2004. Its fault plane solution indi-
cates that it probably did not occur on one of the main,
N–S aligned, Dead Sea faults but on a plane that
deviates 30° anticlockwise off the trend of the Trans-
form (Salamon, 2004). This earthquake, the strongest
one along the DSF since the M
L
= 5.5 earthquake in the
Dead Sea segment on 18.12.1956, released a seismic
moment of 6.5⋅10
23
dyne cm, which is an order of
magnitude greater than the cumulative seismic mo-
ment that had been released in the Dead Sea segment
during the preceding 20 years. In hindsight, it may be
that the gradual decrease in seismic activity along the
DSF during 1991–2000, as well as the slight increase
in seismic activity along the DSF after 1999 that could
be discerned after 2003 (Fig. 7C), could have served as
an indication for increasing probability of the occur-
rence of a strong earthquake after 2003.
The correlation between rate of seismicity (normal-
ized to slip rate) and fault offset (Fig. 12) signifies a
gradual process of decreased seismicity along the DSF
on the scale of millions of years. For other faults, such
decrease was explained by the continuous, long-term
elimination of irregularities (Wesnouski, 1990; Stirling
et al., 1996). Hence, the rate of seismicity along strike-
slip faults evolves with time, and we may now apply
this analysis to the Dead Sea Fault as well. This long-
term evolution of seismicity means that the present
seismic activity along a strike-slip fault system is the
result of both its initial fault pattern and the unidirec-
tional slow process through which it becomes less
complex, with earthquakes converging towards its
main faults (Ben-Zion et al., 1999). This means that
the present seismicity of these strike-slip faults is
affected by their past.
ACKNOWLEDGMENTS
Helpful suggestions by G. Baer, Y. Ben Zion, A.
Hofstetter, V. Lyakhovsy, A. Shapira, and A. Salamon
are gratefully acknowledged. Comments by two anony-
mous reviewers contributed much to the improvement
of the manuscript. We thank D. Steinberg for his help
with some statistical aspects of the study. We are
grateful to L. Feldman for her effective asstance.
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