Several major earthquakes struck Romania in the last century, and all of them occurred in the Vrancea zone in the southeast Carpathian Mountains (Figure l). These earthquakes claimed many lives and caused extensive damage. In the 1977 earthquake alone, 1,570 people died and more than 11,300 were injured, 32,900 apartments were completely destroyed or severely damaged, and economic loss was estimated at more than $2 billion.
To study the crustal and uppermost mantle structure beneath this seismic high-risk area, two major active-source seismic experiments were carried out in 1999 and 2001, nearly 30 years after the last seismic investigations across the eastern Carpathians in the 1970s. The joint seismic refraction and reflection field effort conducted in August and September 2001 (Figure 1), which used almost 800 stand-alone recorders, is one example of the productive interaction forged during the 1999 experiment [Hauser et al., 2001].