Bulletin of the Seismological Society of America
Volume 67 -- Number 6 -- pp 1607 - 1613 -- December 1977


By M. Vered and H. L. Striem



A detailed macroseismic study of the July 11, 1927 earthquake was carried out. A quantitative analysis of damage data provided a correlation for estimating (MM) intensities: I = 6.4 + 1.2 log (percentage of damaged houses). Using axis lengths and areas bounded by the ensuing isoseismal lines, the depth 116 to 28 km) of the event was estimated, and its probable epicenter located near Damiya bridge on the Jordan river. A comparison with the equivalent parameters, inferred from instrumental records, shows agreement between both sets of results and thus confirms the validity of the approach used in the macroseismic study.

The same procedure of studying macroseismic data was applied to an earlier (January 1, 1837) destructive earthquake. It was found that this latter event originated in the upper crust, eastward of Safed, with a 6.25 to 6.5 magnitude.

The isoseismals of both these major earthquakes are elongated in a north-south direction, along the major structural trend in the area. The southern coastal plain of Israel seems generally less vulnerable to Jordan Rift Valley earthquakes than inland regions of similar epicentral distances, though local pockets of anomalous intensities are observed for both earthquakes.


Major earthquakes are, fortunately, relatively rare in Israel. Yet, a study of such events is indispensable for seismic risk evaluation programs in Israel. Therefore, the investigation of earthquakes in pre-instrumental era is essential. Such investigations are necessarily composed of analyses of macroseismic observations. The interpretation of such studies is often imprecise.

The major earthquake of November 7, 1927 provides a unique opportunity, in that it was both instrumentally recorded and macroseismically reported. In this paper We give the results of a detailed macroseismic study of the July 11, 1927 earthquake (Vered and Striem, 1976a, hereafter referred to as VS-I). A critical comparison of macroseismic and instrumental epicenter location and estimates of event depth, vindicates the rationale, methods and correlations used in the macroseismic study. Once established, these procedures of studying macroseismic data were applied to an earlier (January 1, 1837) destructive event (Vered and Striem, 1976b, hereafter referred to as VS-II).

The implications of both these Jordan Rift Valley earthquakes on seismic risk evaluations in Israel are discussed.


Macroseismic observations of the July 11, 1927 earthquake are mostly concerned with two effects of the event: the number of casualties and the damage to buildings. We found, in agreement with accepted practice, that the former does not provide a useful measure of the local effects of the event. Therefore, one is limited to analysis of the damage reports. These must be divided into two classes: (1) descriptions of damage to Arab villages and towns, and (2) details of damage to Jewish settlements and occasionally to structures dating back to the Crusaders. The great difference in building codes, workmanship and materials between the two classes of buildings (Willis, 1928) necessitates using different scales for interpreting the damage. Such scales are provided by the various building type classifications included in the HIM scale, 1956 version (Richter, 1958). Arab buildings belong apparently to class D while Jewish buildings may be classified as class C.

In order to translate the damage reports into meaningful and consistent intensity values, some refinement and subdivision of the MM scale (class D buildings indicator) is clearly needed. Such an attempt is described in detail in VS-I.

After assigning intensity values to Arab villages, we tried to develop a quantitative scale. We defined a damage index (denoted hereafter as DI),

       Number of class D buildings destroyed X 100
DI = ---------------------------------------
                 Total number of class D buildings

The number of buildings destroyed was obtained from the various reliable damage reports (VS-I). The total number of buildings was taken from the official contemporary census. One may then correlate our DI and the intensity values, to obtain

I (MM) = 6.4 + 1.2 log (DI)

Equation (1), which should not be taken too literally but rather as a shorthand notation, is valid over the intensity range VII to IX. It may be applied to localities where the damage is evenly distributed.

Using the intensity ratings thus obtained, an intensity map of the 1927 event was drawn (Figure 1). The map agrees with most of the data, though a very few intensity values do not fit it. These apparently "misfit" values are probably due to some local effects and should not detract from the general validity of the intensity map.

Several parameters of interest may be inferred from Figure 1. The epicenter of the event is found to be located near the Damiya bridge, the earthquake probably originating in the Jordan Rift fault system.

Another parameter of interest is the depth of the 1927 event. We used two of Med- vedev's (1962) methods: a procedure of interpreting the epicentral distance to the isoseismal lines, and a! formula giving the depth of the event in terms of the areas bounded by the second and third isoseismals. Since the isoseismals of the 1927 event are elliptic, we applied Medvedev's methods to both the short and long axes of the ellipses, thus estimating both lower and upper bounds for the focal depth.

The depth h thus obtained, depends on the value of n, the distance exponential coefficient assumed in the calculations. We chose that value of n which minimizes the fluctuations in the various estimates of h obtained from the various isoseismals and found n =1.5.

Using Figure 1, the focal depth of the 1927 event is estimated to be 16 to 28 km

The macroseismically determined parameters of the 1927 event compare quite favorably with the instrumentally derived values. The macroseismically determined epicenter, near the Damiya bridge, is some 10 km from the instrumental determi- nation, 32.0NN, 35.5E I(SS, 1927; Ben-Menahem et al., 1976). Focal depth is estimated as 16 to 28 km (macroseismic data) and as 5 to 7 km with a vertical extent of some 10 km (Ben-Menahem et al., 1976). The agreement between instrumental and macroseismic results both justifies and verifies our methods of analyzing the macroseismic data.

We have tried (VS-I) to estimate the magnitude of the 1927 event from the macroseismic data, by relating areas within various isoseismal lines to local magnitudes. For this purpose, we have used the relations given by Toppozada (1975) for California and Western Nevada. This method gave somewhat higher magnitudes than the instrumentally determined value M = 6.25, Gutenberg and Richter, 1948; Ben-Menahem et al., 1976). The reason for this discrepancy is probably that Toppozzada's results do not hold for our region. Nevertheless, we note for future reference, that a 6.25 M Jordan-Rift earthquake is associated with AVIII = 3200, AVII = 14000 and AVI = 39500 km2, where AN is defined as the area shaken at intensity N or greater.

Having established the validity of our method we applied it (see VS-II) to the Safed earthquake of January 1, 1837 for which no instrumental data exist. The ensuing intensity map is shown as Figure 2, from which we obtain, using the above described procedures, h =7 to 17 km, the epicenter of the event was probably along the Jordon Rift fault system, eastward of Safed.

From the intensity map of this event, we have AVIII = 4000, AVII = 15000 km square, i.e., slightly larger shaken areas at the various intensity levels than the corresponding values for the 1927 event (AVIII = 3200, AVII = 14000 km). Since both events originated at roughly the same depth (upper crust), we conclude that the 1837 event was of the same or slightly higher magnitude than the 1927 event, i.e., it had a magnitude ML = 6.25 to 6.5.

These results are in agreement with the general observations and predictions of Ben-Menahem et al. (1976) concerning the seismicity of the Afro-Eurasian junction.

A phenomenon common to both these recent major Jordon Rift Valley earthquakes is the elliptical appearance of the iso-seismals, which are elongated in a roughly N-S direction. Intensity attenuation along this direction was one intensity unit per 30 km (1837 event) or per 45 km (1927 event). Localities along the southern coast of Israel suffered less than expected on the basis of N-S attenuation rate (Figures 3, 4, and 5). The southern coastal plain suffered apparently less than localities symmetric to it with respect to the epicenter. It seems therefore that this region, which is being considered for accomodating Israel's first nuclear power plant, is the least vulnerable to effects of the Jordon Rift Valley earthquakes, at least in the frequency range to which old Arab houses are sensitive.

It must be remarked, however, that localities of anomalous intensities, relative to adjacent areas, manifest themselves in the data. The so-called "pockets," which are of rather small extent, may suffer either anomalously high (e.g., Reina and Ramle-Lod in the 1927 event) or low (e.g., Kafr Kenna in the 1837 event) intensities. Thus, interpolation of intensity data to specific sites should not be relied upon.


A detailed macroseismic study of the July 11, 1927 earthquake was carried out. The macroseismically determined epicenter and depth of the event are compared with those inferred from instrumental records. The reasonable agreement of both sets of results confirm the validity of the rationale, method, and correlations used in the macroseismic study. An objective local damage index scale, which correlates with the MM scale, was developed.

Once established, these procedures of studying macroseismic data were applied to an earlier (January 1, 1837) destructive event. It is found that this latter event originated in the upper crust, eastward of Safed, with a magnitude ML = 6.25 to 6.5.

The southern coastal plain of Israel is found to be the region least vulnerable to the effects of the Jordan Rift Valley earthquakes. However, the existence of local pockets of anomalous intensities which are inherent in the data, precludes attempts to estimate by interpolation intensity values at specific sites.


This paper expresses the personal opinions of the authors and does not necessarily represent the opinion of the Israel Atomic Energy Commission.

We wish to thank an anonymous reviewer for making some helpful remarks and suggestions.

The two unpublished reports referred to in this paper (VS-I, VS-II), are available upon request from the authors.


Ben-Menahem A., A. Nur, M. Vered (1976). Tectonics, seismicity and structure of the Afro-Eurasian junction--the breaking of an incoherent plate. Phys. Earth Planet Interiors 12, 1-50.

Gutenberg, B. and C. F. Richter (1948). The Seismicity of the Earth, Princeton University Press, Princeton, NJ.

Medvedev, S. V. (1962). Engineering Seismology (English Translation), Israel Program for Scientific Translations, Jerusalem, 1965.

Richter, C. F. (1958). Elementary Seismology, Freeman and Co., San Francisco and London.

Toppozada, T. R. (1975). Earthquake magnitude as a function of intensity data in California and Western Nevada. Bull. Seism. Soc. Am. 65, 1223-1238.

Vered, M. and H. L. Striem (1976a). A macroseismic study of the July 11, 1927 earthquake. Israel Atomic Energy Commission, Report IA-LD-1-107.

Vered, M. and H. L. Striem (1976b). The Safed earthquake of 1.1.1837 and its implications on seismic risk evaluations in Israel. Israel Atomic Energy Commission, Report IA-LD-1-105.

Willis, B. (1928). Earthquakes in the Holy Land. Bull. Seism. Soc. Am. 18, 73-103.