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UCL Institute for Risk and Disaster Reduction


Earthquake surface measurements reveal new revelations about how faults rupture

Joanna PFaure Walker12 November 2018

PhD student Francesco Iezzi (Birkbeck College), supervised by Prof Gerald Roberts (Birkbeck College) and Dr Joanna Faure Walker (UCL IRDR), has published a paper that could revolutionalise how geologists and seismic hazard modellers use long established scaling relationships between fault lengths and surface rupture parameters.

The paper is freely available to all and can be found here.

What new observations have been made?

For five earthquakes studied, the surface fault slip (the amount the fault surface moved during the earthquake) and the throw (the vertical component of the slip) was higher where there was a bend along the length of the fault.

Following the central Italy August and October 2017 earthquakes that ruptured the ground surface, we made detailed high spatial resolution measurements of surface fault displacement along the length of the surface fault ruptures. A study of the amount of vertical and horizontal displacement that occurred along the length of the fault revealed that the throw and slip that occurred during the earthquakes increased where there are bends in the fault. This result is critical and has not been identified before for individual earthquakes.

Damage in Amatrice from the August 2016 Earthquake. Photograph take during EEFIT fieldwork by Dr Joanna Faure Walker.

Why does this occur?

We hypothesis that this occurs in order to maintain the horizontal strain (change in length relative to the original length) across a fault during an earthquake and the long-term horizontal strain-rate that accumulates from multiple earthquakes over thousands of years.

Are there other examples of this?

We then went back and studied other examples earthquakes where there was enough information to determine whether a similar pattern of higher throw and slip could be seen across bends in the fault. In the three further events studied in USA Basin and Range, Greece, and Mexico, we found the same relationship. So it seems this phenomenon occurs worldwide in normal (extensional) faults.

This was the first time that the change in vertical component of slip during an earthquake has been shown to be predictable. However, the observed relationship of increased throw across fault bends has been identified previously in long-term displacements that have accumulated over 15 thousand years as a result of multiple earthquakes in Italy (Faure Walker et al., 2009, Wilkinson et al., 2015). Before now, it was not known whether this increase was caused by there being more earthquakes across the bends or more movement during individual events.  We now know that there can be more slip during individual events, however we do not know whether this is the only mechanism for creating a long-term higher throw-rate across the bends.

What does this mean for earthquake science?

This paper suggests that slip during an earthquake will change where there is a bend along the length of the fault and this change can be quantified and predicted using the proposed theory. This means that close to the fault, earthquakes may be more damaging near a bend in the fault. This finding suggests that we cannot use fault scaling relationships between fault length and expected slip in earthquakes without consideration of fault geometry. This paper can also explain much of the scatter seen in existing plots of maximum surface slip against fault length because when collecting the data as input for such relationships, consideration was not given about whether the measurements were taken across fault bends or not.

These changes in slip along faults in individual earthquakes related to the fault geometry should be included in probabilistic seismic hazard assessments (PSHA).

What other research in the IRDR relates to this?

This work contributes to the IRDR and colleagues’ work on investigating fault behaviour to improve our understanding of earthquake hazard. Recent papers have demonstrated the importance of including detailed fault geometry and slip-rates in seismic hazard calculations (Faure Walker et al., 2018) and Coulomb stress transfer calculations (Mildon et al., 2016, 2017).

Iezzi et al (2018), Coseismic Throw Variation Across Along‐Strike Bends on Active Normal Faults: Implications for Displacement Versus Length Scaling of Earthquake Ruptures, Journal of Geophysical Research, https://doi.org/10.1029/2018JB016732 

Italian Earthquakes, Large and Small

SerenaTagliacozzo6 September 2016

O 1693 c’ha succirutu!

E si n’ha ghiutu lu Vallu ri NuotuUntitled

S’u u pi sorti an-Catania iti

Ciù ri milli voti lacrimati!

Catania ca era ciù perfunna

Ricca ri –ngegnu e ri storia ornata

Spincitivi l’ate a truviriti

L’afflitta virgine a batiuoti.*

(Burderi 2014)

Traditional poem on the M 7.4 earthquake that struck Sicily in 1693, killing about 60,000 people and totally destroying towns such as Noto and Grammichele


In Italy damaging earthquakes occur on average once every 19 months, and seismic disasters happen about once every four years

The M6.2 earthquake of 24th August 2016 in central Italy occurred at 03:36 hrs local time and had a hypocentral depth of about 4 km. At least 281 people were killed, with the highest total at Amatrice (pop. 2,646) in the Province of Rieti (Region of Lazio). This event occurred in a predominantly rural area of the Apennines, and the population of the area of major damage was a mere 4,500 people. As a whole, the event recalls the M5.2 seismic disaster of May 1984 in the Abruzzi National Park (140 km south of Amatrice), in which three people died and 11,000 were left homeless (Alexander 1986). In terms of damage to schools, it recalls the M6.0 earthquake of October 2002 at San Giuliano di Puglia, 182 km from Amatrice, in which 27 children and three teachers were crushed to death when a school collapsed (Langenbach and Dusi 2004). In Amatrice the collapse of a school prompted the same questions about the seismic resistance of educational facilities, and the quality of seismic upgrading as had been raised at San Giuliano (Grant et al. 2007). There are possible indications of corruption and that, according to correlation studies, is the principal cause of seismic disasters, world-wide (Escaleras et al. 2007, Ambraseys and Bilham 2011).

In Italy, the immediate political response to the 2016 Amatrice disaster involved a great many fine words and pious hopes about prevention, reconstruction and the preservation of culture. With respect to previous earthquakes, there were some improvements in the organisation and planning of post-event recovery, notably in cultural heritage protection. However, the sums of money offered to the affected area were by no means large enough to accomplish what the politicians said should happen. Italy is the largest beneficiary of the European Union solidarity fund, and in times of seismic disaster it has also drawn heavily on regional support grants. This has not always meant that the use of the funds has met with EU approval—see the conclusions of the European Court of Auditors’ report on the 2009 L’Aquila earthquake (ECA 2012).

Typically in Italy, events such as the 2016 Amatrice earthquake do not lead to a sustained government response, for there are too many other demands upon the public purse. Commonly, the public part of reconstruction funding is largely gleaned from European funds or else is tacked onto parliamentary bills designed to fund other things, in what Americans call ‘pork-barrel legislation’. At best, a government may wait until the financial climate is more favourable before it allocates significant funding to recovery. Thus it was three years before the first stirring of reconstruction occurred in L’Aquila after the M6.3 earthquake of 2009. Public debt incurred in reconstruction after the 1968 Belice Valley, western Sicily, earthquakes, will not be paid off until 2038, 70 years after the disaster. Belice, moreover, had to wait 15 years before reconstruction even started (Parrinello 2013).

These are the minor events. People suffer no less in them than they do in the major ones, but the overall picture is quite different.

Alexander, D.E. 1986. Disaster Preparedness and the 1984 Earthquakes in Central Italy. Natural Hazards Working Paper no. 57, NHRAIC, University of Colorado, Boulder, Colorado, 90 pp.

Ambraseys, N. and R. Bilham 2011. Corruption kills. Nature 469: 153-155.

Burderi, M. 2014. Il terremoto del 1693 nella pietà popolare. Archivio degli Iblei, July 2014: 1-13. (archiviodegliiblei.it

ECA 2012. The European Union Solidarity Fund’s Response to the 2009 Abruzzi Earthquake: the Relevance and Cost of Operations. Special Report no. 24, Publication Office, European Court of Auditors, Luxembourg 52 pp.

Escaleras, M., N. Anbarci and C.A. Register 2007. Public sector corruption and major earthquakes: a potentially deadly interaction. Public Choice 132: 209-230.

Grant, D.N., J.J. Bommer, R. Pinho, G.M. Calvi, A. Goretti and F. Meroni 2007. A prioritization scheme for seismic intervention in school buildings in Italy. Earthquake Spectra 23(2): 291-314.

Langenbach, R. and A. Dusi 2004. On the cross of Sant’Andrea: the response to the tragedy of San Giuliano di Puglia following the 2002 Molise, Italy, earthquake. Earthquake Spectra 20(S1): S341-S358.

Parrinello, G 2013. The city-territory: large-scale planning and development policies in the aftermath of the Belice valley earthquake (Sicily, 1968). Planning Perspectives 28(4): 571-593.