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The earthquake size distribution follows, in most instances, a power law 1 , 2 , with the slope of this power law, the ‘ b value’, commonly used to describe the relative occurrence of large and small events (a high b value indicates a larger proportion of small earthquakes, and vice versa). Statistically significant variations of b values have been measured in laboratory experiments, mines and various tectonic regimes such as subducting slabs, near magma chambers, along fault zones and in aftershock zones 3 . However, it has remained uncertain whether these differences are due to differing stress regimes, as it was questionable that samples in small volumes (such as in laboratory specimens, mines and the shallow Earth's crust) are representative of earthquakes in general. Given the lack of physical understanding of these differences, the observation that b values approach the constant 1 if large volumes are sampled 4 was interpreted to indicate that b = 1 is a universal constant for earthquakes in general 5 . Here we show that the b value varies systematically for different styles of faulting. We find that normal faulting events have the highest b values, thrust events the lowest and strike-slip events intermediate values. Given that thrust faults tend to be under higher stress than normal faults we infer that the b value acts as a stress meter that depends inversely on differential stress.

The number of fatalities and injured was calculated, using the computer code QLARM and its data set and assuming information about the Irpinia 1980 earthquake became available in near-real-time. The casualties calculated for a point source, an approximate line source and a well-defined line source would have become available about 30 min, 60 min and years after the main shock, respectively. The first estimate would have been satisfactory, indicating the seriousness of the disaster. The subsequent loss estimate after 60 min would have defined the human losses accurately, and the ultimate estimate was most accurate. In 2009, QLARM issued a correct estimate of the number of fatalities within 22 min of the M6.3 L’Aquila main shock. These two results show that the number of casualties and injuries in large and major earthquakes in Italy can be estimated correctly within less than an hour by using QLARM.

Earthquake survivors could be rescued more quickly if the media communicated the number of likely fatalities from the outset, argues Max Wyss.

The Landers earthquake in June 1992 redistributed stress in southern California, shutting off the production of small earthquakes in some regions while increasing the seismicity in neighboring regions, up to the present. This earthquake also changed the ratio of small to large events in favor of more small earthquakes within about 100 kilometers of the epicenter. This implies that the probabilistic estimate for future earthquakes in southern California changed because of the Landers earthquake. The location of the strongest increase in probability for large earthquakes in southern California was the volume that subsequently produced the largest slip in the magnitude 7.1 Hector Mine earthquake of October 1999.

We have compiled a new catalogue of earthquake fatalities for the world, covering the period 856 BC to March 2022, listing 2795 reports. We estimate that the reporting of fatal earthquakes is complete for events with more than 16 fatalities since 1927. The total number of fatalities recorded is 8,336,526. 117 countries have reported at least one earthquake with one fatality or more. 77 and 52 countries have reported more than 100 and 1000 earthquake fatalities, respectively. Caution has to be exercised in estimating what earthquake disasters are in store for a given country because the 95 year period of high quality recording is about an order of magnitude shorter than return times of great earthquakes. Nevertheless, we introduce the earthquake potency for a country, defined as the sum of recorded fatalities divided by the number of earthquakes that it took to accumulate them, which equals the average earthquake disaster size in a given country, in units of fatalities per event. Potency is listed based on all known fatal earthquakes and also based on those since 1927. Both lists have their shortcomings, but provide estimates of what size of future earthquake disaster is likely in store for a particular country. For rescue purposes, it is important to realize that small earthquake, M 5 ± 0.5, can cause significant numbers of fatalities.

The number of fatalities in the Gorkha M7.8 earthquake of April 25, 2015, has been estimated at four different times as follows. In March 2005, the fatality estimate in this journal was 21,000–42,000 with an assumed magnitude of 8.1 (Wyss in Nat Hazard 34:305–314, 2005 ). Within hours after this earthquake, the estimated number of fatalities by QLARM was 2000–10,000 using a point source model and M7.9. Four hours later, the estimate was 20,000–100,000, based on a first approximation line source model and assuming children were in school. Children out of school, as this was a weekend day, reduced the fatalities by approximately a factor of two, but was not taken into account for the calculation. The final line source estimates based on M7.8 and M7.9 calculates 800–9300 and 1100–11,200 fatalities, respectively. The official count is about 10,000 fatalities. These estimates were performed using QLARM, a computer tool and world data set on the distribution of people in settlements and containing a model of the buildings present. It is argued here that the loss estimate 10 years before the event being within a factor of 2.1 of the eventual loss count is useful for mitigation planning. With varying quality of information on the source and the attenuation, the estimates of fatalities shortly after the earthquake are accurate enough to be useful for first responders. With full knowledge of the rupture properties and the regional attenuation of seismic waves, the numbers of human losses are estimated correctly.

Kyrgyzstan is an earthquake-prone country at the border of the Pamir Thrust, north of the active shortening structure of the Pamir Mountains and the intra-continental mountain belt of the Tian Shan further north. The region has had several M7 + damaging earthquakes, which have killed thousands of people. In the West, the country is cut through by the 700-km-long NW–SE Talas-Fergana active strike-slip fault system, where no major earthquakes have been observed in the last 250 years even though paleoseismic studies show the potential to produce M7.0 + events. This study is the second part of a project to estimate the potential damage and losses on residential buildings as well as critical infrastructures in the case of a large earthquake in the two mining towns of Kadamjay and Aidarken in the SW of Kyrgyzstan. Microtremors were recorded on 82 sites and analyzed with the Horizontal-to-Vertical Spectral Ratio (HVSR) method. For each site, we estimate the average frequency of the clearest peak and its amplitude in the HVSR spectra to produce microzonation maps, in terms of response frequency. We further used these data for the calculation of ground shaking using a set of six seismic scenarios based on the known faults around the two towns. This approach has proved to be efficient in a country where the resources and available data are limited and when the time of investigation is short. The Kadamjay and Aidarken cities have been divided into different zones with specific predominant resonance frequency ranges, which information is useful for risk analysis, mitigation and buildings retrofit. In Kadamjay, three regions dominate which are related to the history of alluvial deposition in a series of terraces. The more elevated terrace could be the place of seismic site amplification. Aidarkan is much more homogenous in terms of thickness and type of alluvial deposits.

Given that more than 90% of earthquake fatalities occur in rural environments, one has to rethink how to protect the population. With most rural buildings being one- and two-story dwellings, the earthquake closet (EC) offers an affordable solution as a protection unit. Two recent earthquakes with nearly 100,000 fatalities each are used for estimating the lives that could be saved and how much this would cost. The cost of constructing an EC in a single-family home is taken to be$500–$ 600 in developing countries. For the “statistical value of life”$1 million is used, a minimum amount given in the literature. The cost of hospitalization is derived from reports after an earthquake. The number of fatalities and injured avoided is estimated for an example earthquake each in China and Pakistan. The estimated dollar savings resulting in large earthquakes reach $ 18.3 billion at a cost of$1.3 billion, and $ 10 billion at a cost of $0.5 billion, respectively, in the two examples.

Seismic hazard maps are constructed by extrapolating from the frequency of small earthquakes, the annual probability of large, infrequent, earthquakes. Combining the potential contribution from all seismically active volumes, one calculates the peak ground acceleration with a probability to be exceeded by 10 % in 50 years at any given point. The consequential risk, the losses to be expected, derives from the damage the calculated shaking causes to buildings, and the impact on occupants due to collapsing structures. We show that the numbers of fatalities in recent disastrous earthquakes were underestimated by the world seismic hazard maps by approximately two to three orders of magnitude. Thus, seismic hazard maps based on the standard method cannot be used to estimate the risk to which the population is exposed due to large earthquakes.

The 2015 M7.8 Gorkha earthquake has moved the upper, unbroken, part of the Main Himalayan Thrust (MHT) and the neighboring sections of this fault closer to failure. Using the program and data set of QLARM, which has been correct in fatality estimates of past Himalayan earthquakes, we estimate quantitatively the numbers of fatalities, injured and strongly affected people when assumed ruptures along these two sections will happen. In the Kathmandu up-dip scenario with M8.1, we estimate that more than 100,000 people may perish, about half a million may be injured, and 19 million are likely to be affected strongly, if we assume the high virtual attenuation observed for the 2015 Gorkha earthquake exists here also. Likewise, if the 100 km underthrusting segment west of Gorkha ruptures, we quantitatively estimate that 12,000–62,000 people may perish and 4 million to 8 million will be strongly affected, in a down-dip (lower half of the thrust plane) and an up-dip rupture (upper half) scenario, respectively. If the up-dip part of the MHT cannot rupture by itself, and greater earthquakes are required to generate the several meters of displacement observed in trenches across the MHT, then our estimates are minima.