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Bulletin of the Seismological Society of Amenca, Vol 71, No 2, pp. 573-574, April 1981

B O O K R E V I E W

EARTHQUAKE HISTORY OF ETHIOPIA AND THE HORN OF AFRICA, by Pmrre Gouin,International Development Research Centre, Box 8500, Ottawa, Canada, 1979, 258 pp., $18.00

The selsmicity of an area can be determmed m two ways: directly by observing earthquakesinstrumentally, and indirectly, by evaluating historical records of felt earthquakes as well as by investi-gating the Holocene geologic record. Observational seismology and the resulting catalogs of instrumen-tally recorded earthquakes have existed only since the turn of the century. Despite the fact thatmicroselsmmity is considered to be a good reflection of macroseismicity, we are still heavily reliant onhistorical records (and wh erever possible, geologic information from trenching) for an accurate picture ofthe long-term seismic activity of an area and especially of major earthquakes. For example, NicholasAmbraseys has shown the value of a long historical record of earthquakes m identifying changes inseismmity m t he eastern Med iterr anean during time frames of hundr eds of years. Of course, such longhlston cal records are not available for many regions.

Although the presen t selsmmlty of Africa is known from epicenter determ inati ons made teleselsmically,the fust oncal selsmicity is poorly known. Thus, "'Earthquake History of Ethlopm and the Horn of Africa"

by Pmrre Goum, which contains a carefully researched history of earthquakes m nort heast ern Africa foralmost 6 centuries before 1977, is an Important contribution. In large part, the book represen ts 30 yearsof observations by the author, who founded the Geological Observatory in Addis Ababa. It is, m effect,an an notat ed version of the author 's data file on selsmm and volcanic activity in nort heast ern Africa.

The file consists of two sectmns. The first contains fustoncal, cultural, geological, and inst rumenta l{where available) mformatmn on the varmus earthquakes. Gouin discusses m detail the fundamentalproblem of dating historic events, especmlly m relation to the many "eras" in Ethiopmn culture, thestructure of the Ethiopian calendar, and the use of solar echpses; he also discusses the problems ofIdentifying lustoric locations. The second part of the file consists of a co mput er printo ut listing of seismicand volcanic activity for which some parameters such as magmtude, epicenter location, or intensit y couldbe calculated. In th e final sectmn of the book, the available record is evaluated and th e uncerta inties arediscussed

The file opens with the first known written document on actlwty m E thm pia --th e eruptmn, accom-pained by damaging earthquakes, of Dubbl Volcano near t he City of Asseb on the R ed Sea in 1400 A.DThe coverage for later centuries is inevitably uneven. Temporally, it ranges from scant references bychronicle writers to the continuous momtormg by present-day mstrnments. Spatially, the record isheavily biased toward the northern regions of Ethiopia; m these parts, the admmistratmn was usuallylocated, and monastic libraries could preserve their manuscnpts throughout long periods of war anddevastation It was in this area too tha t the first geological investigations were made in th e early 1900's

Goum pomts out that the coverage of earthquakes m Ethmpm is also mformatmnally uneven.Hlstormns probably reported only the largest tremors, those that had an effect on settled areas.Earthquakes were ~nportant when they could be used to impress on the people a landmark in history,such as a battle, a coronation, an astronommal phenom enon (e g., an eclipse), or even a perso n's age.Goum descnbes the example of the Guraghe natron which lives on the western escarpment of the

Ethiopian rift valley and whose old people still reckon their age in terms of so many years "after theearthquakes that were thought to mark the end of the world" (the earthquakes of August 1906).

Goum considers that there is a fugh probabihty that the largest earthquakes that have taken place innorthern Ethmpla during the last 500 years have been reported. On the other hand, the lack of writtenevidence from the southern part of Ethiopia cannot be Interpreted as mdmatmg the absence of selsmmactivity. Gouin points out the usefulness of an oral history passed down through th e cent uries e g., theGalla tribes have legends about localities that presumably were destroyed by seismic tremors and thatare now covered by lakes, such legends are heard all along the Ethmpian rift. Although oral fustoryprovides httle mformatmn on the magnitude and epmenter of earthquakes, it does provide mformationtha t serves as a ch eck on: (1) the valid ity of maxlm um- amp htu de ~ersus t~ne-o f-occurre nce curves, and(2) statistmal extrapolations based on shorter sampling intervals. In fact, one of the reasons for theprese nt book was that Gouin wanted to extend the 75-year earthquake file tha t he ha d felt was adequate

to repre sent presen t and near-future selsmiclty in "Seismic Zoning m Et hmpl a" pub hshed by the AddisAbaba Observatory in 1976 Thus, all the primary and secondary sources of mformatmn for tfuscompanmn volume, on wh ich the statistical analyses of regional seismic and volcanic hazards in E thmpl awere based, are now ~ven. In addition, Goum needed to pu t the 75-year sampling window into a largerhistorical perspective to see whether present seismic actlwty is anomalous and whether statlstmal

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574 BOOK REVI EW

predictions are borne out by historical evidence Of course, as Gouin admits, the m terp retat lons arepersonal, and alternativ e solut, ons are possible from the same set of data.

In t he scheme of plate tectonics, Ethiopia occupies a key position because it is at the junction of threerift syst ems- -th e Ethiopian, the Red Sea, and the Gulf of Aden rafts--tha t are caused by a stationary hotspot In the underlying mantle. During the 30-million-year history of this tmple junction, seismic andvolcamc noise must hav e been mo re or less continuous m the failed Ethio pian rift, and it will undoubtedl y

continue for many centuries to come. As complete an earthquake h istor y of the ki nd that Goum has treedto p resen t is a necessity if adequate seismm zonmg codes axe to be designed for power plants, industry,and pollution centers in thin developing par t of Africa

HENRYSPALL

U. S. GEOLOGICAL SURVEYRESTON, VIRGINIA 22092

Manusc ript received Novem ber 10, 1980