Israel Journal of Earth-Sciences
Volume 42 -- pp. 93 - 96

A new estimate for the epicenter of the Jericho earthquake of 11 July 1927

By Avi Shapira, Ron Avni, and Amos Nur
Shapira: Seismological Division, The Institute for Petroleum Research and Geophysics, P.O.Box 2286,58122 Holon, Israel

Avni: Department of Geography and Environmental Development, Ben-Gurion University of the Negev, 84105 Beer Sheva, Israel

Nur: Department of Geophysics, Stanford University, Stanford, CA 94305, USA

(Received 1 June 1993 and in revised form 10 August 1993)


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[EPICENTRAL MAP]
[REFERENCES]
[COPYRIGHT INFORMATION]

The strongest and most destructive earthquake to hit the Holy Land during the current century occurred on 11 July 1927 and is known as the Jericho earthquake. Its magnitude was estimated by Ben-Menahem et al. (1976) to be 6.25. Shapira (1979) left this estimate unchanged, although the Ms value was determined as 5.9. Recent evaluations of the effects of this earthquake (Vered and Striem, 1977) yield a maximum intensity MM = IX in the Jordan Valley close to the Damia Bridge on the Jordan River.

In all publications which refer to the Jericho earthquake, the epicentral location quoted is 32.0 degrees N, 35.5 degrees E, i.e., a few kilometers south of the Damia Bridge and 30 km north of Jericho. Consequently, it was assumed that the earthquake ruptured a fault segment between Damia and the northern part of the Dead Sea, which is a part of the Dead Sea transform. This assumption has been used in seismo-tectonic studies (see for example BenMenahem et al., 1976; Ben-Menahem, 1979; Shapira, 1983; Arieh and Rotstein, 1985; Rotstein, 1987; Arieh and Rabinowitz, 1989; Yucemen, 1992) as well as earthquake hazard assessments for countries neighboring the Jordan Valley.

The original source for the location of the epicenter of the Jericho earthquake is the ISS (Intemational Seismological Summary) Bulletin of 1927. The ISS also provides arrival-time information from several tens of stations around the world. Apparently, however, these data were not used in the past for locating the earthquake, the location of the 11 July 1927 earthquake being quoted from the seismological station in Ksara, Lebanon. It is very probable that this location was esthimated from the three component station in Ksara (although S-arrivals at Ksara are not reported in the ISS Bulletin) and was greatly influenced by the reports of destruction in Nablus.

Here we report for the first time on the instrumental determination of the Jericho earthquake epicenter, applying standard location procedures using the arrival-time data.

When calculating the arrival-time residuals to stations which reported arrival- times up to a distance of 40 from the previously published location of 32 degrees N,35.5 degrees E, we find an unacceptably large number which suggest that the previous location is incorrect. To obtain a better fit, we have relocated the earthquake, yielding the new location 60 km south of the previously determined one. In this determination we have omitted those readings which yield residuals greater than +10 s. The final results are shown in Table 1.

To estimate the uncertainty and stability of the results, we have randomly excluded 3 arrival-time data at a time from the computations and obtained new solutions based on the smaller data sets. We may conclude that the best estimate for the epicenter location of the 11 July 1927 earthquake is 31.6 degrees N 35.4 degrees E (190/110 Israel grid) with an estimated uncertainty of _ 10 km. In Fig . 1, a map of the foci of epicenters located by the national network during the period 1981-1992, we show the old reported and the new computed epicentral locations of the Jericho earthquake (the uncertainty ellipse is also shown). We are currently collecting additional information regarding the locations of the fore- and aftershocks of this earthquake.

The instrumentally-deterrnined epicenter, in the northern Dead Sea basin instead of the Damia area, may better fit the macroseismic observations of this event. Re-evaluated intensities, to be published by us separately, show that the severest effects were along the northern coast of the Dead Sea including the occurrence of seiche (Abel, 1927) and the appearance of fissures on the northern coast. All other macroseismic observations are equally acceptable for an epicenter located anywhere betweeen the Damia Bridge area and Ein Bokek, since intensities are not as much influenced by the distance of the main cities located in the epicentral area from the epicenter itself as by local geotechnical conditions, especially landslides on unstable slopes (Wachs and Levitte, 19 .78). In both old and new epicenter locations, Jericho is the closest city; intensities in more distant cities (for both possible epicenters) are often much higher. Nevertheless, despite the uncertainty inherent in instrumental epicenter determination, it should be considered as far more accurate than the inferred location from macroseismic data.

Taking into account the difficulties associated with synchronization of the mechanical clocks in 1927 and the relatively low sensitivity of the seismic stations, the obtained solutions is reasonably accurate. By assuming that the earthquake should have occurred somewhere along the Dead Sea rift system, the poor station configuration (most of the recording stations are in Europe) would not greatly influence the results Since their main contribution to uncertainty is in the E-W direction, whereas the location along the N-S direction is much more constrained.

EPICENTRAL MAP

Figure 1. Map showing the relocated epicenter of the Jericho earthquake and its uncertainty ellipse. Also shown is the seismicity around this epicenter during 1981-1992.

[Small Map Showing Newly Calculated Epicenter]

REFERENCES

Abel, F.M.1927. Le recent tremblement de terre en Palestine. Revue Biblique 36: 571-578.

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

Arieh, E., Rotstein, Y.1985. A note on the seismicity of Israel (19061982). Bull. Seism. Soc. Am. 75: 881-887.

Ben-Menahem, A. 1979. Earthquake catalog for the Middle East (92 BC-1980 AD). Boll. Geofis. Teor. Appl. 84: 245313.

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

International Seismological Summary. 1927. University of Oxford.

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

Shapira, A.1979. Re-determined magnitudes of earthquakes in the Afro-Eurasian junction. Isr. J. Earth Sci. 28: 107-109.

Shapira, A. 1983. Potential earthquake risk estimations by application of a simulation process. Tectonophysics 95: 75-89.

Vered, M., Striem, H.L. 1977. A macro-seismic study and implications of structural damage of two recent major earthquakes in the Jordan rift. Bull. Seism. Soc. Am. G7: 1607-1613.

Wachs, D., Levitte, D. 1978. Damage caused by landslide during the earthquakes of 1837 and 1927 in the Galilee region. Geol. Surv. Isr. Rep. HY/1/80, 7 pp.

Yucemen, M.S. 1992. Seismic hazard maps for Jordan and vicinity. Nat. Hazards 6: 201-226.